Unfortunately the answer is not simple. RadTreeListView filtering treats all items as a "flat"collection and disregards their level in hierarchy .
Although there is no clean solution to your requirement there might be a small hack - e.g. add a property to your items - e.g. Level property . When filtering you may add a filtering condition with and/or clause to include exclude items based on their level .
The final composite filtering condition should be something like : All items that match criteria or have level ==0.
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