diff --git a/src/ITensorNetworks.jl b/src/ITensorNetworks.jl
index fdc479c7..a0efd7ff 100644
--- a/src/ITensorNetworks.jl
+++ b/src/ITensorNetworks.jl
@@ -42,7 +42,7 @@ include("solvers/local_solvers/dmrg_x.jl")
 include("solvers/local_solvers/contract.jl")
 include("solvers/local_solvers/linsolve.jl")
 include("treetensornetworks/abstracttreetensornetwork.jl")
-include("treetensornetworks/ttn.jl")
+include("treetensornetworks/treetensornetwork.jl")
 include("treetensornetworks/opsum_to_ttn.jl")
 include("treetensornetworks/projttns/abstractprojttn.jl")
 include("treetensornetworks/projttns/projttn.jl")
diff --git a/src/abstractitensornetwork.jl b/src/abstractitensornetwork.jl
index 4961cfe8..2dc983ee 100644
--- a/src/abstractitensornetwork.jl
+++ b/src/abstractitensornetwork.jl
@@ -617,7 +617,11 @@ function neighbor_vertices(ψ::AbstractITensorNetwork, T::ITensor)
 end
 
 function linkinds_combiners(tn::AbstractITensorNetwork; edges=edges(tn))
-  combiners = DataGraph(directed_graph(underlying_graph(tn)); vertex_data_eltype=ITensor, edge_data_eltype=ITensor)
+  combiners = DataGraph(
+    directed_graph(underlying_graph(tn));
+    vertex_data_eltype=ITensor,
+    edge_data_eltype=ITensor,
+  )
   for e in edges
     C = combiner(linkinds(tn, e); tags=edge_tag(e))
     combiners[e] = C
diff --git a/src/edge_sequences.jl b/src/edge_sequences.jl
index 65e8ac8f..e9086ce2 100644
--- a/src/edge_sequences.jl
+++ b/src/edge_sequences.jl
@@ -1,7 +1,7 @@
 using Graphs: IsDirected, connected_components, edges, edgetype
 using ITensors.NDTensors: Algorithm, @Algorithm_str
 using NamedGraphs: NamedGraphs
-using NamedGraphs.GraphsExtensions: undirected_graph
+using NamedGraphs.GraphsExtensions: GraphsExtensions, undirected_graph
 using NamedGraphs.PartitionedGraphs: PartitionEdge, PartitionedGraph, partitioned_graph
 using SimpleTraits: SimpleTraits, @traitfn, Not
 using SimpleTraits
@@ -26,7 +26,9 @@ end
 end
 
 @traitfn function edge_sequence(
-  ::Algorithm"forest_cover", g::::(!IsDirected); root_vertex=NamedGraphs.default_root_vertex
+  ::Algorithm"forest_cover",
+  g::::(!IsDirected);
+  root_vertex=GraphsExtensions.default_root_vertex,
 )
   forests = NamedGraphs.forest_cover(g)
   edges = edgetype(g)[]
diff --git a/src/solvers/alternating_update/alternating_update.jl b/src/solvers/alternating_update/alternating_update.jl
index 8fae9532..3b0f6b77 100644
--- a/src/solvers/alternating_update/alternating_update.jl
+++ b/src/solvers/alternating_update/alternating_update.jl
@@ -1,5 +1,6 @@
 using ITensors: state
 using ITensors.ITensorMPS: linkind
+using NamedGraphs.GraphsExtensions: GraphsExtensions
 using Observers: Observers
 
 function alternating_update(
@@ -13,7 +14,7 @@ function alternating_update(
   sweep_printer=nothing,
   (sweep_observer!)=nothing,
   (region_observer!)=nothing,
-  root_vertex=default_root_vertex(init_state),
+  root_vertex=GraphsExtensions.default_root_vertex(init_state),
   extracter_kwargs=(;),
   extracter=default_extracter(),
   updater_kwargs=(;),
diff --git a/src/solvers/sweep_plans/sweep_plans.jl b/src/solvers/sweep_plans/sweep_plans.jl
index 208f9bce..69221995 100644
--- a/src/solvers/sweep_plans/sweep_plans.jl
+++ b/src/solvers/sweep_plans/sweep_plans.jl
@@ -1,3 +1,6 @@
+using Graphs: AbstractEdge, dst, src
+using NamedGraphs.GraphsExtensions: GraphsExtensions
+
 direction(step_number) = isodd(step_number) ? Base.Forward : Base.Reverse
 
 function overlap(edge_a::AbstractEdge, edge_b::AbstractEdge)
@@ -58,7 +61,7 @@ end
 function forward_sweep(
   dir::Base.ForwardOrdering,
   graph::AbstractGraph;
-  root_vertex=default_root_vertex(graph),
+  root_vertex=GraphsExtensions.default_root_vertex(graph),
   region_kwargs,
   reverse_kwargs=region_kwargs,
   reverse_step=false,
@@ -141,7 +144,10 @@ function default_sweep_plans(
 end
 
 function default_sweep_plan(
-  graph::AbstractGraph; root_vertex=default_root_vertex(graph), region_kwargs, nsites::Int
+  graph::AbstractGraph;
+  root_vertex=GraphsExtensions.default_root_vertex(graph),
+  region_kwargs,
+  nsites::Int,
 )
   return vcat(
     [
@@ -158,7 +164,7 @@ end
 
 function tdvp_sweep_plan(
   graph::AbstractGraph;
-  root_vertex=default_root_vertex(graph),
+  root_vertex=GraphsExtensions.default_root_vertex(graph),
   region_kwargs,
   reverse_step=true,
   order::Int,
diff --git a/src/solvers/tdvp.jl b/src/solvers/tdvp.jl
index 1b70015e..7a58fe1b 100644
--- a/src/solvers/tdvp.jl
+++ b/src/solvers/tdvp.jl
@@ -1,3 +1,5 @@
+using NamedGraphs.GraphsExtensions: GraphsExtensions
+
 #ToDo: Cleanup _compute_nsweeps, maybe restrict flexibility to simplify code
 function _compute_nsweeps(nsweeps::Int, t::Number, time_step::Number)
   return error("Cannot specify both nsweeps and time_step in tdvp")
@@ -101,7 +103,7 @@ function tdvp(
   sweep_printer=nothing,
   (sweep_observer!)=nothing,
   (region_observer!)=nothing,
-  root_vertex=default_root_vertex(init_state),
+  root_vertex=GraphsExtensions.default_root_vertex(init_state),
   reverse_step=true,
   extracter_kwargs=(;),
   extracter=default_extracter(), # ToDo: extracter could be inside extracter_kwargs, at the cost of having to extract it in region_update
diff --git a/src/treetensornetworks/abstracttreetensornetwork.jl b/src/treetensornetworks/abstracttreetensornetwork.jl
index d24c4e95..7b74f0d9 100644
--- a/src/treetensornetworks/abstracttreetensornetwork.jl
+++ b/src/treetensornetworks/abstracttreetensornetwork.jl
@@ -1,6 +1,6 @@
 using Graphs: has_vertex
 using NamedGraphs.GraphsExtensions:
-  edge_path, leaf_vertices, post_order_dfs_edges, post_order_dfs_vertices
+  GraphsExtensions, edge_path, leaf_vertices, post_order_dfs_edges, post_order_dfs_vertices
 using IsApprox: IsApprox, Approx
 using ITensors: @Algorithm_str, directsum, hasinds, permute, plev
 using ITensors.ITensorMPS: linkind, loginner, lognorm, orthogonalize
@@ -21,11 +21,6 @@ end
 ITensorNetwork(tn::AbstractTTN) = error("Not implemented")
 ortho_region(tn::AbstractTTN) = error("Not implemented")
 
-function default_root_vertex(gs::AbstractGraph...)
-  # @assert all(is_tree.(gs))
-  return first(leaf_vertices(gs[end]))
-end
-
 # 
 # Orthogonality center
 # 
@@ -64,7 +59,9 @@ end
 # Truncation
 # 
 
-function Base.truncate(tn::AbstractTTN; root_vertex=default_root_vertex(tn), kwargs...)
+function Base.truncate(
+  tn::AbstractTTN; root_vertex=GraphsExtensions.default_root_vertex(tn), kwargs...
+)
   for e in post_order_dfs_edges(tn, root_vertex)
     # always orthogonalize towards source first to make truncations controlled
     tn = orthogonalize(tn, src(e))
@@ -84,7 +81,9 @@ end
 #
 
 # TODO: decide on contraction order: reverse dfs vertices or forward dfs edges?
-function NDTensors.contract(tn::AbstractTTN, root_vertex=default_root_vertex(tn); kwargs...)
+function NDTensors.contract(
+  tn::AbstractTTN, root_vertex=GraphsExtensions.default_root_vertex(tn); kwargs...
+)
   tn = copy(tn)
   # reverse post order vertices
   traversal_order = reverse(post_order_dfs_vertices(tn, root_vertex))
@@ -98,7 +97,7 @@ function NDTensors.contract(tn::AbstractTTN, root_vertex=default_root_vertex(tn)
 end
 
 function ITensors.inner(
-  x::AbstractTTN, y::AbstractTTN; root_vertex=default_root_vertex(x, y)
+  x::AbstractTTN, y::AbstractTTN; root_vertex=GraphsExtensions.default_root_vertex(x)
 )
   xᴴ = sim(dag(x); sites=[])
   y = sim(y; sites=[])
@@ -186,7 +185,7 @@ end
 
 # TODO: stick with this traversal or find optimal contraction sequence?
 function ITensorMPS.loginner(
-  tn1::AbstractTTN, tn2::AbstractTTN; root_vertex=default_root_vertex(tn1, tn2)
+  tn1::AbstractTTN, tn2::AbstractTTN; root_vertex=GraphsExtensions.default_root_vertex(tn1)
 )
   N = nv(tn1)
   if nv(tn2) != N
@@ -228,14 +227,16 @@ function Base.:+(
   ::Algorithm"densitymatrix",
   tns::AbstractTTN...;
   cutoff=1e-15,
-  root_vertex=default_root_vertex(tns...),
+  root_vertex=GraphsExtensions.default_root_vertex(first(tns)),
   kwargs...,
 )
   return error("Not implemented (yet) for trees.")
 end
 
 function Base.:+(
-  ::Algorithm"directsum", tns::AbstractTTN...; root_vertex=default_root_vertex(tns...)
+  ::Algorithm"directsum",
+  tns::AbstractTTN...;
+  root_vertex=GraphsExtensions.default_root_vertex(first(tns)),
 )
   @assert all(tn -> nv(first(tns)) == nv(tn), tns)
 
@@ -302,7 +303,10 @@ end
 
 # TODO: implement using multi-graph disjoint union
 function ITensors.inner(
-  y::AbstractTTN, A::AbstractTTN, x::AbstractTTN; root_vertex=default_root_vertex(x, A, y)
+  y::AbstractTTN,
+  A::AbstractTTN,
+  x::AbstractTTN;
+  root_vertex=GraphsExtensions.default_root_vertex(x),
 )
   traversal_order = reverse(post_order_dfs_vertices(x, root_vertex))
   ydag = sim(dag(y); sites=[])
@@ -320,7 +324,7 @@ function ITensors.inner(
   y::AbstractTTN,
   A::AbstractTTN,
   x::AbstractTTN;
-  root_vertex=default_root_vertex(B, y, A, x),
+  root_vertex=GraphsExtensions.default_root_vertex(B),
 )
   N = nv(B)
   if nv(y) != N || nv(x) != N || nv(A) != N
@@ -349,8 +353,8 @@ function ITensorMPS.expect(
   operator::String,
   state::AbstractTTN;
   vertices=vertices(state),
-  # ToDo: verify that this is a sane default
-  root_vertex=default_root_vertex(siteinds(state)),
+  # TODO: verify that this is a sane default
+  root_vertex=GraphsExtensions.default_root_vertex(state),
 )
   # TODO: Optimize this with proper caching.
   state /= norm(state)
diff --git a/src/treetensornetworks/opsum_to_ttn.jl b/src/treetensornetworks/opsum_to_ttn.jl
index b4bda869..e257c953 100644
--- a/src/treetensornetworks/opsum_to_ttn.jl
+++ b/src/treetensornetworks/opsum_to_ttn.jl
@@ -4,7 +4,8 @@ using ITensors.ITensorMPS: ITensorMPS, cutoff, linkdims, truncate!
 using ITensors.LazyApply: Prod, Sum, coefficient
 using ITensors.NDTensors: Block, maxdim, nblocks, nnzblocks
 using ITensors.Ops: Op, OpSum
-using NamedGraphs.GraphsExtensions: boundary_edges, degrees, is_leaf, vertex_path
+using NamedGraphs.GraphsExtensions:
+  GraphsExtensions, boundary_edges, degrees, is_leaf, vertex_path
 using StaticArrays: MVector
 
 # convert ITensors.OpSum to TreeTensorNetwork
@@ -522,29 +523,17 @@ Convert an OpSum object `os` to a TreeTensorNetwork, with indices given by `site
 function ttn(
   os::OpSum,
   sites::IndsNetwork;
-  root_vertex=default_root_vertex(sites),
-  splitblocks=false,
-  algorithm="svd",
+  root_vertex=GraphsExtensions.default_root_vertex(sites),
   kwargs...,
-)::TTN
+)
   length(ITensors.terms(os)) == 0 && error("OpSum has no terms")
   is_tree(sites) || error("Site index graph must be a tree.")
   is_leaf(sites, root_vertex) || error("Tree root must be a leaf vertex.")
 
   os = deepcopy(os)
   os = sorteachterm(os, sites, root_vertex)
-  os = ITensorMPS.sortmergeterms(os) # not exported
-  if algorithm == "svd"
-    T = ttn_svd(os, sites, root_vertex; kwargs...)
-  else
-    error("Currently only SVD is supported as TTN constructor backend.")
-  end
-
-  if splitblocks
-    error("splitblocks not yet implemented for AbstractTreeTensorNetwork.")
-    T = ITensors.splitblocks(linkinds, T) # TODO: make this work
-  end
-  return T
+  os = ITensorMPS.sortmergeterms(os)
+  return ttn_svd(os, sites, root_vertex; kwargs...)
 end
 
 function mpo(os::OpSum, external_inds::Vector; kwargs...)
diff --git a/src/treetensornetworks/ttn.jl b/src/treetensornetworks/treetensornetwork.jl
similarity index 94%
rename from src/treetensornetworks/ttn.jl
rename to src/treetensornetworks/treetensornetwork.jl
index a8b3a301..4bca217d 100644
--- a/src/treetensornetworks/ttn.jl
+++ b/src/treetensornetworks/treetensornetwork.jl
@@ -1,7 +1,7 @@
 using Graphs: path_graph
 using ITensors: ITensor
 using LinearAlgebra: factorize, normalize
-using NamedGraphs: vertextype
+using NamedGraphs.GraphsExtensions: GraphsExtensions, vertextype
 
 """
     TreeTensorNetwork{V} <: AbstractTreeTensorNetwork{V}
@@ -76,7 +76,12 @@ function mps(f, is::Vector{<:Index}; kwargs...)
 end
 
 # Construct from dense ITensor, using IndsNetwork of site indices.
-function ttn(a::ITensor, is::IndsNetwork; ortho_region=[default_root_vertex(is)], kwargs...)
+function ttn(
+  a::ITensor,
+  is::IndsNetwork;
+  ortho_region=[GraphsExtensions.default_root_vertex(is)],
+  kwargs...,
+)
   for v in vertices(is)
     @assert hasinds(a, is[v])
   end