[Hackerrank]Inserting a Node Into a Sorted Doubly Linked List

/*
  Insert Node at the end of a linked list 
  head pointer input could be NULL as well for empty list
  Node is defined as 
  class Node {
     int data;
     Node next;
     Node prev;
  }
*/

Node SortedInsert(Node head,int data) {
    Node newNode = new Node();
    newNode.data = data;
    if (head==null)
        return newNode;                 //如果是空表则返回新的节点
    else if (data<=head.data){
        head.prev = newNode;        //如果插入的元素比头节点元素小，就插在头节点
        newNode.next = head;        //前面
        return newNode;
    }
    else {
        Node tmp = SortedInsert(head.next,data);
        tmp.prev = head;
        head.next = tmp;
    }
    return head;
}