The C1RadialMenu control can hold submenus. These submenus are created when C1RadialMenuItems are nested within the tags of other C1RadialMenuItems. For example, placing the following XAML markup

<c1:C1RadialMenuItem Header="First">
     <c1:C1RadialMenuItem Header="Second">
          <c1:C1RadialMenuItem Header="Third">
               <c1:C1RadialMenuItem Header="Fourth">
                    <c1:C1RadialMenuItem Header="Fifth"/>
</c1:C1RadialMenuItem>

between the opening and closing tags of a C1RadialMenu would create the following:

You can have as many nested radial menus as you want, although it's best not to have more than two or three submenus in a hierarchy for usability purposes.