1110. Delete Nodes And Return Forest

class Solution:
    def delNodes(self, root: TreeNode, to_delete: List[int]) -> List[TreeNode]:
        remaining = []
        to_delete = set(to_delete)
        self.remove_node(root,to_delete,remaining)
        if root.val not in to_delete:
            remaining.append(root)
        return remaining
    
    def remove_node(self,root,to_delete,remaining):
        if not root:
            return None
        root.left = self.remove_node(root.left,to_delete,remaining)
        root.right = self.remove_node(root.right,to_delete,remaining)
        if root.val in to_delete:
            if root.left:
                remaining.append(root.left)
            if root.right:
                remaining.append(root.right)
            return None
        return root