code: public List<String> getDependencyPath(int nodeIndex, int rootIndex) {
      TreeGraphNode node = getNodeByIndex(nodeIndex);
      TreeGraphNode rootTree = getNodeByIndex(rootIndex);
      return getDependencyPath(node, rootTree);
    }
docs: Returns the dependency path as a list of String, from node to root, it is assumed that
  that root is an ancestor of node
  
  @return A list of dependency labels