private AVLTree <char, Symbol> CreateCharTree(string text)
        {
            IComparer comparer = new CharComparer();

            var tree = new AVLTree <char, Symbol>(comparer);

            foreach (var symbol in text)
            {
                AddSymbol(symbol, tree);
            }

            return(tree);
        }
        public AVLTree <char, Symbol> CreateCharTree(List <Symbol> symbols)
        {
            IComparer comparer = new CharComparer();

            var tree = new AVLTree <char, Symbol>(comparer);

            foreach (var symbol in symbols)
            {
                AddSymbol(symbol, tree);
            }

            return(tree);
        }