Hello, Elke,
Thank you for writing.
You can find below a sample code snippet demonstrating how to add the subitems in
RadSplitButton:
The following help article demonstrates how to get started with
RadSplitButton and add items:
https://docs.telerik.com/devtools/winforms/buttons/splitbutton/working-with-radsplitbutton-items
Regards,
Dess
Progress Telerik