Doubly Linked List Insertion in a the middle in C++

#include<iostream>
using namespace std;

class Node
{
public:
  int data;
  Node *next;
  Node *prev;
};

class LinkedList
{
private:
  Node * head;
public:
  LinkedList ()
  {				// constructor
    head = NULL;
  }
  int calcSize ();
  void insert (int data);
  void insertMiddle (int data);
  int getLength ();
  void display ();
};

void LinkedList::insert (int data)
{

  Node *newNode = new Node ();

  newNode->data = data;
  newNode->next = head;
  newNode->prev = NULL;

  //If the linked list already had atleast 1 node
  if (head != NULL)
    head->prev = newNode;

  // changing the new head to this freshly entered node
  head = newNode;
}

void LinkedList::insertMiddle (int data)
{

  Node *newNode = new Node ();
  newNode->data = data;

  // if the LL was empty
  if (head == NULL)
    {
      // using insert function to insert at start
      insert (data);
      return;
    }

  // otherwise
  int size = getLength ();

  // find correct insertion position for middle
  int mid = (size % 2 == 0) ? (size / 2) : (size + 1) / 2;

  // will only happen when there is one node in Doubly Linked List
  // we will have to insert at the last, 
  // inserting 2nd node at the last
  // Example size = 1 will result in mid = 1 so entering after 1st node
  // where size itself is 1 so entering last node
  if (mid == size)
    {
      newNode->next = NULL;
      newNode->prev = head;
      head->next = newNode;
      return;
    }

  Node *temp = head;
  // traverse to current mid position
  while (--mid)
    {
      temp = temp->next;
    }

  // (mid+1)th node prev to this newNode
  (temp->next)->prev = newNode;
  // newNode's prev to this current middle node
  newNode->prev = temp;
  // newNode's next to (mid+1)th node
  newNode->next = temp->next;
  // current mid node's next becomes this newNode
  temp->next = newNode;

  // this newNode inserted after the middle node successfully
}

int LinkedList::getLength ()
{
  int len = 0;

  Node *node = head;

  while (node != NULL)
    {
      node = node->next;
      len++;
    }
  return len;
}

//function to print the doubly linked list
void LinkedList::display ()
{
  cout << "\n\n";

  Node *end = NULL;
  Node *node = head;

  cout << "\nList in forward direction: ";
  while (node != NULL)
    {
      cout << node->data << " ";
      end = node;
      node = node->next;
    }

  cout << "\nList in backward direction: ";

  while (end != NULL)
    {
      cout << end->data << " ";
      end = end->prev;
    }
}

int main ()
{
  LinkedList *doubly_list = new LinkedList ();

  doubly_list->insert (120);
  doubly_list->insert (0);

  doubly_list->display ();

  doubly_list->insertMiddle (30);
  doubly_list->display ();

  doubly_list->insertMiddle (60);
  doubly_list->display ();

  doubly_list->insertMiddle (90);
  doubly_list->display ();

  return 0;
}