# 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 pruneTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        def dfs(node: TreeNode) -> int:
            if not node:
                return 0
            
            left = dfs(node.left)
            right = dfs(node.right)
            
            if left == 0:
                node.left = None
            
            if right == 0:
                node.right = None
                
            return left + right + node.val
        
        dummy = TreeNode(-1, root)
        
        dfs(dummy)
        return dummy.left