Merge Sort for Doubly Linked List

class LinkedList {
 
    static Node head;  
 
  
    static class Node {
 
        int data;
        Node next, prev;
 
      
        Node(int d) {
            data = d;
            next = prev = null;
        }
    }
 
    void print(Node node) {
        Node temp = node;
        System.out.println("Forward Traversal using next pointer");
        while (node != null) {
            System.out.print(node.data + " ");
            temp = node;
            node = node.next;
        }
        System.out.println("\nBackward Traversal using prev pointer");
        while (temp != null) {
            System.out.print(temp.data + " ");
            temp = temp.prev;
        }
    }
 
  
    Node split(Node head) {
        Node fast = head, slow = head;
        while (fast.next != null && fast.next.next != null) {
            fast = fast.next.next;
            slow = slow.next;
        }
        Node temp = slow.next;
        slow.next = null;
        return temp;
    }
 
    Node mergeSort(Node node) {
        if (node == null || node.next == null) {
            return node;
        }
        Node second = split(node);
 
        
        node = mergeSort(node);
        second = mergeSort(second);
 
        
        return merge(node, second);
    }
 
 
    Node merge(Node first, Node second) {
       
        if (first == null) {
            return second;
        }
 
       
        if (second == null) {
            return first;
        }
 
       
        if (first.data < second.data) {
            first.next = merge(first.next, second);
            first.next.prev = first;
            first.prev = null;
            return first;
        } else {
            second.next = merge(first, second.next);
            second.next.prev = second;
            second.prev = null;
            return second;
        }
    }
 
   
    public static void main(String[] args) {
 
        LinkedList list = new LinkedList();
        list.head = new Node(10);
        list.head.next = new Node(30);
        list.head.next.next = new Node(3);
        list.head.next.next.next = new Node(4);
        list.head.next.next.next.next = new Node(20);
        list.head.next.next.next.next.next = new Node(5);
         
         
        Node node = null;
        node = list.mergeSort(head);
        System.out.println("Linked list after sorting :");
        list.print(node);
 
    }
}