protected virtual void OnAdded(AddedEventArgs <TKey, TValue> args)
 {
     if (this.Added != null)
     {
         Added(this, args);
     }
 }
 private static void SortedDict_Added(object sender, AddedEventArgs <int, string> e)
 {
     Console.WriteLine($"after adding key: [{e.Key}] value: [{e.Value}]");
 }