Hello Kelley Wong,
You cannot filter with Predicate the way you want in Silverlight. If your tree is databound to ObservableCollection, you can filter the source collection and rebind the tree like so:
ObservableCollection<DataItem> col =
>()(col.Where(x => x.Names.StartsWith(
tree.ItemsSource = col;
If your tree is declarative or created from code behind, you have to iterate over the Items collection and use the Remove method if the RadTreeViewitems meets your condition.
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