code: public void expandRootChildNodes() {
          TreeNode root = (TreeNode) getTreeAlert().getModel().getRoot();
          if (root == null) {
              return;
          }
          TreePath basePath = new TreePath(root);
          for (int i = 0; i < root.getChildCount(); ++i) {
              getTreeAlert().expandPath(basePath.pathByAddingChild(root.getChildAt(i)));
          }
      }
docs: Expands all child nodes of the root node.
  <p>
  This method should be called only from the EDT (Event Dispatch Thread).
  </p>