def insert(key: T) = {
        def recInsert(tree: SplayTree[T]): Node[T] = {
            tree match {
                case Node(l, v, r) if key < v => Node(recInsert(l), v, r)
                case Node(l, v, r) if key > v => Node(l, v, recInsert(r))
                case n: Node[T]               => n
                case _                        => Node(Leaf(), key, Leaf())
            }
        }
        recInsert(this).splay(key)
    }