static void insert(int v, TreeNode root, int depth, int n) {
    if(root == null) {
        return;
    }
    if(depth == n-1) {
        TreeNode temp = root.left;
        root.left = new TreeNode(v);
        root.left.left = temp;
        temp = root.right;
        root.right = new TreeNode(v);
        root.right.right = temp;
    } else {
        insert(v, root.left, depth+1, n);
        insert(v, root.right, depth+1, n);
    }
}

public TreeNode addOneRow(TreeNode root, int v, int d) {
    
    if(d == 1) {
        TreeNode n = new TreeNode(v);
        n.left = root;
        return n;
    }
    
    insert(v, root, 1, d);
    return root;
    
}