Insert items into double linked list in sorted order

sortedDoubleLinkedList

using System;

namespace SortedDoubleLinkedList
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var sortedList = new SortedDoubleLinkedList();
            sortedList.Add(5);
            sortedList.Add(3);
            sortedList.Add(9);
            sortedList.Add(7);
            sortedList.Add(4);
            
            Console.WriteLine("Entries in the list are");
            sortedList.Display();
        }
    }
    
    class Node {
        public Node(int data) {
            Data = data;
        }
        
        public int Data {get; private set;}
        
        public Node Prev {get; set;}
        
        public Node Next {get; set;}
    }

    class SortedDoubleLinkedList {
    
        Node head;
        Node tail;
        
        public void Add(int data) {
            if (head == null) {
                head = new Node(data);
                tail = head;
            } else if (data <= head.Data) {
                addAtHead(data);
            } else if (data >= tail.Data) {
                addAtTail(data);
            } else {
                Node current = head;
                while (current.Next != null) {
                    if ((current.Data < data) && (data <= (current.Next).Data)) {
                        Node newNode = new Node(data);
                        Node next = current.Next;
                        
                        current.Next = newNode;
                        newNode.Prev = current;
                        newNode.Next = next;
                        next.Prev = newNode;
                        break;
                    }
                    
                    current = current.Next;
                }
            }
        }
        
        public void Display() {
            Node current = head;
            while (current != null) {
                Console.Write(current.Data + " ");
                current = current.Next;
            }
            Console.WriteLine();
        }
    
        void addAtHead(int data) {        
            Node newNode = new Node(data);
            newNode.Next = head;
            head.Prev = newNode;
            head = newNode;
        }
        
        void addAtTail(int data) {
            Node newNode = new Node(data);
            tail.Next = newNode;
            newNode.Prev = tail;
            tail = newNode;
        }             
    }
}