LinkedList list = new LinkedList();
    Link link1 = new Link("A");
    list.insert(list.head,link1);
    Link link2 = new Link("B");
    list.insert(link1, link2);
    Link link3 = new Link("C");
    list.insert(link2, link3);
    list.display_List_Start_From_Head();

public void insert(Link currentNode, Link newNode)
    {
        if(head == null)
        {
            head = newNode;
            tail = newNode;
        }
        else
        {
            currentNode.next = newNode;
            newNode.prev = currentNode;
            tail = newNode;
        }


    }