Hi Tamar Amit,
Thank you for the question.
Currently, we do not have an established time frame for the desired control. Generally, we have it in our plans, but it will be ready no earlier than Q2 2010.
For the time being, please find attached a sample project which demonstrates how you can embed a RadTreeView in RadComboBox. Please note that this is not a generic solution and it may not work correctly in all scenarios. Feel free to modify the approach according to your needs.
If you have additional questions, feel free to contact me.
All the best,
the Telerik team