public void Add(Bracket b)
        {
            Node newNode = new Node {
                Value = b
            };

            if (First == null)
            {
                First = newNode;
                Last  = newNode;
            }
            else
            {
                Last.Next        = newNode;
                newNode.Previous = Last;
                Last             = newNode;
            }
        }
 public void Add(Bracket b)
 {
     Node newNode = new Node { Value = b };
     if (First == null)
     {
         First = newNode;
         Last = newNode;
     }
     else
     {
         Last.Next = newNode;
         newNode.Previous = Last;
         Last = newNode;
     }
 }