# class TreeNode:#     def __init__(self, x):#         self.val = x#         self.left = None#         self.right = Noneclass Solution:    def levelOrderBottom(self, root: TreeNode) -> List[List[int]]:        if root is None:            return []                result, current = [], [root]        while current:            next_level, vals = [], []            for node in current:                vals.append(node.val)                if node.left:                    next_level.append(node.left)                if node.right:                    next_level.append(node.right)            current = next_level            result.append(vals)        return result[::-1]