如何修复二叉树级别顺序打印的以下代码

from collections import deque

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def levelOrder(root):
    if not root:
        return []

    result = []
    queue = deque()
    queue.append(root)

    while queue:
        level_size = len(queue)
        level_nodes = []

        for _ in range(level_size):
            node = queue.popleft()
            level_nodes.append(node.val)

            if node.left:
                queue.append(node.left)
            if node.right:
                queue.append(node.right)

        result.append(level_nodes)

    return result