I'm afraid that the RadTreeListView control is designed to work with homogeneous data and some of its functionality may not behave as expected if using a heterogeneous source. You can have a look at the following thread which discusses a similar requirement.
Unfortunately, we do not have any plans for introducing support for such a source. If you would, however, provide more details on your current setup and exact requirement, I'd be more than happy to try and suggest a viable solution for your particular scenario.
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