Tree Mirror:

Python

def tree_mirror(node):
    if not node:
        return
    node.left, node.right = node.right, node.left
    tree_mirror(node.left)
    tree_mirror(node.right)

JavaScript

function treeMirror(node) {
    if (!node) {
        return;
    }
    let temp = node.left;
    node.left = node.right;
    node.right = temp;
    treeMirror(node.left);
    treeMirror(node.right);
}