code: protected BehaviorTree<?> retrieveArchetypeTree (String treeReference) {
  		BehaviorTree<?> archetypeTree = repository.get(treeReference);
  		if (archetypeTree == null) {
  //			if (assetManager != null) {
  //				// TODO: fix me!!!
  //				// archetypeTree = assetManager.load(name, BehaviorTree.class, null);
  //				repository.put(treeReference, archetypeTree);
  //				return null;
  //			}
  			archetypeTree = parser.parse(resolver.resolve(treeReference), null);
  			registerArchetypeTree(treeReference, archetypeTree);
  		}
  		return archetypeTree;
  	}
docs: Retrieves the archetype tree from the library. If the library doesn't contain the archetype tree it is loaded and added to
  the library.
  @param treeReference the tree identifier, typically a path
  @return the archetype tree.
  @throws SerializationException if the reference cannot be successfully parsed.