Supposing that you want to do custom filtering and you don't want to change the ViewModels, I suggest you to do re-binding when you filter. For instance, you can dynamically change the ItemsSource of the RadTreeView by first making a copy of the initial data and then filtering it or using a Linq methods
that return IEnumerable when applied to ObservableCollection (probably the type of your ItemsSource collection). Please let us know if this is suitable for you.
the Telerik team
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