Left View of Binary Tree

6    queue = deque([root])
●    while queue:
8        level_size = len(queue)
9        for i in range(level_size):
10            node = queue.popleft()
11            if i == 0: ans.append(node.data)
12            if node.left: queue.append(node.left)
13            if node.right: queue.append(node.right)
14    return ans