public static void main(String[] args) {
        // TreeNode root =  BuildTree.buildTree();
        TreeNode root =  new TreeNode(1);
        List<List<Integer>> result = new Binary_Tree_Zigzag_Level_Order_Traversal().zigzagLevelOrder(root);
        for (int i=0; i< result.size();i++ ) {
            System.out.println(result.get(i));
        }
        System.out.println("Hello world");
    }