public TreeNode parent(TreeNode subTree, TreeNode element) {
        if (subTree == null)
            return null;
        if (subTree.left == element || subTree.right == element)
            // 返回父结点地址
            return subTree;

        TreeNode p;
        // 现在左子树中找，如果左子树中没有找到，才到右子树去找
        if ((p = parent(subTree.left, element)) != null)
            // 递归在左子树中搜索
            return p;
        else
            // 递归在右子树中搜索
            return parent(subTree.right, element);
    }