public DuplexLinkedList(T data)
        {
            var item = new DuplexItem <T>(data);

            Head  = item;
            Tail  = item;
            Count = 1;
        }
        public void Add(T data)
        {
            var item = new DuplexItem <T>(data);

            if (Count == 0)
            {
                Head  = item;
                Tail  = item;
                Count = 1;
                return;
            }

            Tail.Next     = item;
            item.Previous = Tail;
            Tail          = item;
            Count++;
        }