diff --git a/pmml-h2o/src/main/java/org/jpmml/h2o/SharedTree.java b/pmml-h2o/src/main/java/org/jpmml/h2o/SharedTree.java
index cafbbcb..836f230 100644
--- a/pmml-h2o/src/main/java/org/jpmml/h2o/SharedTree.java
+++ b/pmml-h2o/src/main/java/org/jpmml/h2o/SharedTree.java
@@ -27,6 +27,8 @@ public interface SharedTree {
 
 	byte[] getCompressedTreeAux();
 
+	Integer nextId();
+
 	SharedTreeMojoModel.AuxInfo getAuxInfo(int id);
 
 	void encodeAuxInfo(Node node, double score, double recordCount);
diff --git a/pmml-h2o/src/main/java/org/jpmml/h2o/SharedTreeMojoModelConverter.java b/pmml-h2o/src/main/java/org/jpmml/h2o/SharedTreeMojoModelConverter.java
index 69be459..0ac415f 100644
--- a/pmml-h2o/src/main/java/org/jpmml/h2o/SharedTreeMojoModelConverter.java
+++ b/pmml-h2o/src/main/java/org/jpmml/h2o/SharedTreeMojoModelConverter.java
@@ -23,6 +23,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Function;
 
 import com.google.common.collect.Iterables;
@@ -81,6 +82,9 @@ public List<TreeModel> encodeTreeModels(Schema schema){
 
 			SharedTree sharedTree = new SharedTree(){
 
+				private AtomicInteger idSequence = new AtomicInteger(0);
+
+
 				@Override
 				public byte[] getCompressedTree(){
 					return compressedTree;
@@ -91,6 +95,11 @@ public byte[] getCompressedTreeAux(){
 					return compressedTreeAux;
 				}
 
+				@Override
+				public Integer nextId(){
+					return this.idSequence.getAndIncrement();
+				}
+
 				@Override
 				public SharedTreeMojoModel.AuxInfo getAuxInfo(int id){
 					return auxInfos.get(id);
@@ -138,7 +147,7 @@ protected void ensureRecordCount(Node node, double recordCount){
 	public TreeModel encodeTreeModel(SharedTree sharedTree, PredicateManager predicateManager, Schema schema){
 		Label label = new ContinuousLabel(DataType.DOUBLE);
 
-		Node root = encodeNode(sharedTree, null, 0, True.INSTANCE, new CategoryManager(), predicateManager, schema);
+		Node root = encodeNode(sharedTree, null, sharedTree.nextId(), True.INSTANCE, new CategoryManager(), predicateManager, schema);
 
 		TreeModel treeModel = new TreeModel(MiningFunction.REGRESSION, ModelUtil.createMiningSchema(label), root)
 			.setMissingValueStrategy(TreeModel.MissingValueStrategy.DEFAULT_CHILD);
@@ -155,9 +164,6 @@ public Node encodeNode(SharedTree sharedTree, ByteBufferWrapper byteBuffer, Inte
 		}
 
 		SharedTreeMojoModel.AuxInfo auxInfo = sharedTree.getAuxInfo(id);
-		if(auxInfo == null){
-			throw new IllegalArgumentException();
-		}
 
 		int nodeType = byteBuffer.get1U();
 
@@ -171,7 +177,7 @@ public Node encodeNode(SharedTree sharedTree, ByteBufferWrapper byteBuffer, Inte
 			double score = byteBuffer.get4f();
 
 			Node result = new CountingLeafNode(score, predicate)
-				.setId(id);
+				.setId(toNodeId(auxInfo != null, id));
 
 			return result;
 		}
@@ -255,7 +261,7 @@ public Node encodeNode(SharedTree sharedTree, ByteBufferWrapper byteBuffer, Inte
 
 		Node leftChild;
 
-		Integer leftId = auxInfo.nidL;
+		Integer leftId = (auxInfo != null ? auxInfo.nidL : sharedTree.nextId());
 
 		ByteBufferWrapper leftByteBuffer = new ByteBufferWrapper(compressedTree);
 		leftByteBuffer.skip(byteBuffer.position());
@@ -268,7 +274,7 @@ public Node encodeNode(SharedTree sharedTree, ByteBufferWrapper byteBuffer, Inte
 			double score = leftByteBuffer.get4f();
 
 			leftChild = new CountingLeafNode(score, leftPredicate)
-				.setId(leftId);
+				.setId(toNodeId(auxInfo != null, leftId));
 		} else
 
 		{
@@ -277,7 +283,7 @@ public Node encodeNode(SharedTree sharedTree, ByteBufferWrapper byteBuffer, Inte
 
 		Node rightChild;
 
-		Integer rightId = auxInfo.nidR;
+		Integer rightId = (auxInfo != null ? auxInfo.nidR : sharedTree.nextId());
 
 		ByteBufferWrapper rightByteBuffer = new ByteBufferWrapper(compressedTree);
 		rightByteBuffer.skip(byteBuffer.position());
@@ -306,25 +312,30 @@ public Node encodeNode(SharedTree sharedTree, ByteBufferWrapper byteBuffer, Inte
 			double score = rightByteBuffer.get4f();
 
 			rightChild = new CountingLeafNode(score, rightPredicate)
-				.setId(rightId);
+				.setId(toNodeId(auxInfo != null, rightId));
 		} else
 
 		{
 			rightChild = encodeNode(sharedTree, rightByteBuffer, rightId, rightPredicate, rightCategoryManager, predicateManager, schema);
-		}
+		} // End if
 
-		sharedTree.encodeAuxInfo(leftChild, auxInfo.predL, auxInfo.weightL);
-		sharedTree.encodeAuxInfo(rightChild, auxInfo.predR, auxInfo.weightR);
+		if(auxInfo != null){
+			sharedTree.encodeAuxInfo(leftChild, auxInfo.predL, auxInfo.weightL);
+			sharedTree.encodeAuxInfo(rightChild, auxInfo.predR, auxInfo.weightR);
+		}
 
 		Node result = new CountingBranchNode(null, predicate)
-			.setId(id)
+			.setId(toNodeId(auxInfo != null, id))
 			.setDefaultChild(leftward ? leftChild.getId() : rightChild.getId())
 			.addNodes(leftChild, rightChild);
 
-		if(id == 0){
-			float weight = (auxInfo.weightL + auxInfo.weightR);
+		if(auxInfo != null){
 
-			sharedTree.encodeAuxInfo(result, (auxInfo.predL * auxInfo.weightL + auxInfo.predR * auxInfo.weightR) / weight, weight);
+			if(id == 0){
+				float weight = (auxInfo.weightL + auxInfo.weightR);
+
+				sharedTree.encodeAuxInfo(result, (auxInfo.predL * auxInfo.weightL + auxInfo.predR * auxInfo.weightR) / weight, weight);
+			}
 		}
 
 		return result;
@@ -360,6 +371,11 @@ public int getNTreesPerGroup(SharedTreeMojoModel model){
 		return (int)getFieldValue(FIELD_NTREESPERGROUP, model);
 	}
 
+	static
+	private Integer toNodeId(boolean hasAux, Integer id){
+		return (hasAux ? id : id + 1);
+	}
+
 	private static final Field FIELD_COMPRESSEDTREES;
 	private static final Field FIELD_COMPRESSEDTREESAUX;
 	private static final Field FIELD_NTREEGROUPS;