Thank you for contacting us! By default context menu is displayed only vertical. However, you can easily customize its appearance by applying style for its items template panel:
I have prepared sample project demonstrating how to achieve this. In addition, I have modified the template of the menu to prevent stretching it on the screen width. (as I assume this scenario is related to this - http://www.telerik.com/community/forums/change-width-of-contextmenu)
Regards,
Tsvyatko
Telerik
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