public IEnumerator<T> GetEnumeratorYieldThree()
        {
            yield return Value;
            if (Left != null)
                foreach (var elem in Left)
                    yield return elem;
            if (this.Right != null)
                foreach (var elem in this.Right)
                    yield return elem;
        }
        public IEnumerator<T> GetEnumeratorYieldFour()
        {
            var q = new Queue<BinaryTreeNode<T>>();
            q.Enqueue(this);
            while (q.Count > 0)
            {
                BinaryTreeNode<T> current = q.Dequeue();
                yield return current.Value;
                if (current.Left != null) q.Enqueue(current.Left);
                if (current.Right != null) q.Enqueue(current.Right);
            }
        }
        public IEnumerator<T> GetEnumerator()
        {
            if (enumtype <= 2)
                return new BTEnum<T>(this);
            else if (enumtype == 3)
                return GetEnumeratorYieldThree();
            else if (enumtype == 4)
                return GetEnumeratorYieldFour();
            else return new BTEnum<T>(this);
        }
        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }