# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
        levels = []
        queue = [root]
        while queue:
            level = []
            newQueue = []
            for node in queue:
                if node != None:
                    level.append(node.val)
                    newQueue.append(node.left)
                    newQueue.append(node.right)
            if level:
                levels.append(level)
            queue = newQueue
        return levels