public class AVLTree<TKey, TValue>
        where TKey : IComparable<TKey>
    {
        Node<TKey, TValue> _root;
        public int Count { get; private set; }

        public void Add(TKey key, TValue value)
        {
            throw new NotImplementedException();
        }

        public bool Remove(TKey key)
        {
            throw new NotImplementedException();
        }

        protected TValue GetValue(TKey key)
        {
            throw new NotImplementedException();
        }

        protected TValue SetValueByKey(TKey key, TValue newValue)
        {
            throw new NotImplementedException();
        }

        protected void TreeBalance()
        {
            throw new NotImplementedException();
        }

        public TValue this[TKey index]
        {
            get => GetValue(index);
            set => SetValueByKey(index, value);
        }
    }