def level_order(node: TreeNode) -> None:
    if not isinstance(node, TreeNode) or not node:
        return
    q: queue.Queue = queue.Queue()
    q.put(node)
    while not q.empty():
        node_dequeued = q.get()
        print(node_dequeued.data, end=",")
        if node_dequeued.left:
            q.put(node_dequeued.left)
        if node_dequeued.right:
            q.put(node_dequeued.right)