linkedList c#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            link<int> a = new link<int> { };
            a.addFirst(a,new node<int>(1));
            a.add(????);
        }
    }
    class node<T>
    {
        public T data;
        public node<T> next;
        public node(T data)
        {
            this.data = data;
        }
    }
    class link<T>
    {
        node<T> firstNode;
        public void add(node<T> node, node<T> newNode)
        {
            newNode.next = node.next;
            node.next = newNode;
        }
        public void addFirst(link<T> link, node<T> newNode)
        {
            newNode.next = link.firstNode;
            link.firstNode = newNode;
        }
        public void removeAfter(node<T> node)
        {
            node.next = node.next.next;
        }
        public void removeBeggining(link<T> link)
        {
            if (link.firstNode.next != null)
            {
                link.firstNode = link.firstNode.next;
            }
        }

    }
}