# More Code
class Solution:
    def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:

        if root is None:
            return root

        if not root.left and not root.right:
            return root

        root.left = self.invertTree(root.left)
        root.right = self.invertTree(root.right)

        tmp = root.left
        root.left = root.right
        root.right= tmp

        return root


# Simpler
class Solution:
    def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:

        if root is None:
            return

        left = self.invertTree(root.right)
        right = self.invertTree(root.left)
        root.left, root.right = left, right

        return root