ListCloneExtension.cs

   public static class ListExtension
    {
        public static List<T> CloneList<T>(this List<T> list, List<T> oldlist)
        {
            BinaryFormatter formatter = new BinaryFormatter();
            MemoryStream stream = new MemoryStream();
            formatter.Serialize(stream, oldlist);
            stream.Position = 0;

            return (List<T>)formatter.Deserialize(stream);
        }
    }