public static void New(this ITrackableObject source, ITrackableObject parent = null)
        {
            var tracker = source.StartTracking();

            if (parent != null)
            {
                var parentTracker = GetTracker(parent);
                foreach (var subscriber in parentTracker.OnChanged)
                {
                    tracker.OnChanged.Add(subscriber);
                }
            }
            tracker.Added = true;
        }