Resolves #30 adding button in a "+" menu

index.html

@@ -141,6 +141,17 @@ <h4>EDAM is a simple ontology of well established, familiar concepts that are pr
             <button type="button" class="btn btn-default"
                     onclick="browser.interactive_tree().cmd().resetPanAndZoom()">Reset zoom
             </button>
+            <div class="btn-group dropup">
+                <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown"
+                        aria-haspopup="true" aria-expanded="false">
+                    <i class="fa fa-plus"></i>
+                </button>
+                <ul class="dropdown-menu">
+                    <li><a href="#" onclick="browser.interactive_tree().cmd().expandAllDescendantElement()">Expand all tree</a></li>
+                    <!--<li role="separator" class="divider"></li>-->
+                    <!--<li><a href="#">Separated link</a></li>-->
+                </ul>
+            </div>
             <div class="pull-right">
                 <dl class="dl-horizontal meta-info">
                     <dt>Current version</dt>