As the feature is not supported out-of-the-box, I would recommend the following approach :
An external TextBox with handler for the TextChangedEvent. Within the EventHandler you may perform search over the data model ( the ItemsSource of RadTreeListView) . I believe it is easy to find the corresponding item in any collection. Then having the Item , you may call BringIntoView or BringIntoViewAsync methods of RadTreeListView , and then set the current cell of RadTreeListView.
This is jut a general explanation of the recommended approach. In case you have troubles implementing it , just give me a runnable application with a RadTreeListView bound to some sample data matching your business objects , and I will implement it there for you . ( To be able to attach a project , please open a support ticket ) .
All the best,
the Telerik team