void build(TreeNode node, List<List<Integer>> result, int lvl) {
		if (node == null)
			return;
		if (lvl > result.size()) {
			LinkedList<Integer> lvlResult = new LinkedList<Integer>();
			result.add(lvlResult);
		}
		result.get(lvl - 1).add(node.val);
		build(node.left, result, lvl + 1);
		build(node.right, result, lvl + 1);

	}