DefaultMutableTreeNode obj = new DefaultMutableTreeNode("Object Layer");
root.add(obj);
addNodes(obj, getSortedTileSets(EditorModel.OBJECT_LAYER), "", 0, expand);
// notify the JTree that we've put some brand new branches on it.
model.reload();
// expand our container categories
for (TreePath treePath : expand) {
_tsettree.expandPath(treePath);
}