@Override
      public void treeExpanded(TreeExpansionEvent event) {
        TreePath path = event.getPath();
        TreeModel model = tree.getModel();
        Object lastPathComponent = path.getLastPathComponent();
        if (model.getChildCount(lastPathComponent) == 1) {
          TreePath firstChildPath = path.pathByAddingChild(model.getChild(lastPathComponent, 0));
          tree.expandPath(firstChildPath);
        }
      }
@Override
      public void treeExpanded(TreeExpansionEvent event)