public class ObservableCollection2<T> : ObservableCollection<T>
    {
        public void AddRange(IEnumerable<T> items)
        {
            InsertRange(Count, items);
        }
        public void InsertRange(int index, IEnumerable<T> items)
        {
            int count = 0;
            foreach(var item in items)
            {
                base.Items.Insert(index + (count++), item);
            }
            OnPropertyChanged(new PropertyChangedEventArgs("Count"));
            OnPropertyChanged(new PropertyChangedEventArgs("Items[]"));
            OnCollectionChanged(
                new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add,
                changedItems: (System.Collections.IList)items.ToList(),
                startingIndex: index));
        }
    }