Can we just do the regular BFS level by level and then reverse at the end of each level?

frontier = deque()
frontier.append(root)
visited = set()
level = 0
while frontier:
    next_frontier = deque()
    curr_level = []
    for curr_node in frontier:
        visited.add(curr_node)
        curr_level.append(curr_node.val)
        if curr_node.left and curr_node.left not in visited:
            next_frontier.append(curr_node.left)
        if curr_node.right and curr_node.right not in visited:
            next_frontier.append(curr_node.right)
      
    if not level % 2 == 0:
		    curr_level = curr_level[::-1]
    result.append(curr_level)
    frontier = next_frontier
    level += 1