code: private void prettyPrint(Node<K, V> n) {
      if (n.left != null) {
        prettyPrint(n.left);
      }
      System.out.println(n);
      if (n.right != null) {
        prettyPrint(n.right);
      }
    }
docs: Recursively prints the tree.
  
  @param n the node to start recursion at