private static void ChildToAggregateMapUnmap <T>(this ConcurrentObservableCollection <T> source, ConcurrentObservableCollection <T> dest, MapUnmap mapUnmap)
        {
            NotifyCollectionChangedEventHandler collectionChangedHander = (s, e) =>
            {
                foreach (var item in e?.OldItems?.OfType <T>() ?? Enumerable.Empty <T>())
                {
                    dest.Remove(item);
                }
                foreach (var item in e?.NewItems?.OfType <T>() ?? Enumerable.Empty <T>())
                {
                    dest.Add(item);
                }
            };

            using (var freezeToken = source.FreezeUpdates())
            {
                if (mapUnmap == MapUnmap.Map)
                {
                    dest.AddRange(source);
                    source.CollectionChanged += collectionChangedHander;
                }
                else if (mapUnmap == MapUnmap.Unmap)
                {
                    dest.RemoveRange(source);
                    source.CollectionChanged -= collectionChangedHander;
                }
            }
        }
        public static void MapChildListToAggregate <T, K>(this ConcurrentObservableCollection <T> source, ConcurrentObservableCollection <K> dest, Func <T, ConcurrentObservableCollection <K> > selectChildList)
        {
            NotifyCollectionChangedEventHandler collectionChangedHander = (s, e) =>
            {
                foreach (var item in e?.OldItems?.OfType <T>() ?? Enumerable.Empty <T>())
                {
                    selectChildList(item).UnmapChildToAggregate(dest);
                }
                foreach (var item in e?.NewItems?.OfType <T>() ?? Enumerable.Empty <T>())
                {
                    selectChildList(item).MapChildToAggregate(dest);
                }
            };

            using (var freezeToken = source.FreezeUpdates())
            {
                source.CollectionChanged += collectionChangedHander;
                foreach (var item in source)
                {
                    selectChildList(item).MapChildToAggregate(dest);
                }
            }
        }