把二叉树打印成多行

import java.util.ArrayList;
/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;
    }
}
*/
public class Solution {
    ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> list = new ArrayList<>();
        depth(pRoot, 1, list);
        return list;
    }
    public void depth(TreeNode node, int depth, ArrayList<ArrayList<Integer>> list) {
        if(node == null) return;
        if(depth > list.size()) list.add(new ArrayList<Integer>());
        list.get(depth-1).add(node.val);
        depth(node.left, depth + 1, list);
        depth(node.right, depth + 1, list);
    }
}