function leftRightRotation(node) {
  leftRotation(node.left);
  return rightRotation(node);
}
Left Right Rotation (LR Rotation)

@example LR rotation on node 3
       4                       4
     /                        /                           4
   3                         3*                          /
 /                          /                           2
1*   --left-rotation(1)->  2   --right-rotation(3)->  /  \
 \                        /                          1    3*
  2                      1

@param {TreeNode} node
   this is the node we want to rotate to the right. E.g., node 3
@returns {TreeNode} new parent after the rotation