Incorrect Doubly Linked List

List.cpp

#include <memory>
#include <string>
#include <iostream>

using namespace std;

template <typename K, typename V>
struct Node
{
  K key;
  V value;
  std::shared_ptr<Node<K, V>> prev;
  std::shared_ptr<Node<K, V>> next;

  Node(K&& key, V&& value) : key(std::move(key)), value(std::move(value)) {}
};

template <typename K, typename V>
struct List
{
  typedef Node<K, V> node_t;
  typedef std::shared_ptr<node_t> node_ptr;
  
  List() : head{}, tail{} {}

  void insertBefore(
      // const std::shared_ptr<T>& is incorrect. we must use std::shared_ptr<T> here.
      const node_ptr& node,
      const node_ptr& newNode)
  {
    newNode->prev = node->prev;
    newNode->next = node;
    if (node->prev) {
      node->prev->next = newNode;
    } else {
      head = newNode;
    }
    node->prev = newNode;
  }

  node_ptr head;
  node_ptr tail;
};
  
int main()
{
  List<int, string> list;

  list.head = std::make_shared<Node<int, string>>(1, "a");
  list.insertBefore(
      list.head,
      std::make_unique<Node<int, string>>(2, "b")
  );
  list.insertBefore(
      list.head,
      std::make_unique<Node<int, string>>(3, "c")
  );

  // we expect the output should be 3 2 1 but get 2 3 2.
  cout << list.head->key << endl;
  cout << list.head->next->key << endl;
  cout << list.head->next->next->key << endl;
  return 0;
}

at LINE 38, node and newNode arguments references to the same pointer.