Improve TransformToTree to use with AutoRefresh on parent id property

[chuuddo]

Now we can use AutoRefresh method instead of recreating whole object to update tree when object implement INotifyPropertyChanged and parent id changed.

_cache.Connect()
    .AutoRefresh(x => x.ParentId)
    .TransformToTree(x => x.ParentId)
    .AsObservableCache();