BST, pointers, not balanced

#include <bits/stdc++.h>
using namespace std;

struct Node
{
  int key;
  Node * left, * right;
  Node(int pkey): key(pkey), left(nullptr), right(nullptr) {}
};

Node * root = nullptr;

bool exists(Node * node, const int & key)
{
  if (node == nullptr) return false;
  if (node->key == key) return true;
  return exists(node->left, key) || exists(node->right, key);
}

void insert(Node * &node, const int & key)
{
  if ( !node ) node = new Node(key);
  else
  {
    if ( key < node->key )
      insert(node->left, key);
    if ( key > node->key )
      insert(node->right, key);
  }
}

int depth(Node * node)
{
  if (!node) return 0;
  return max(depth(node->left), depth(node->right)) + 1;
}

int main()
{
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  // freopen("input.txt", "r", stdin);
  int x;
  while (true)
  {
    cin >> x;
    if(!x) break;
    insert(root, x);
  }
  cout << depth(root);
}