Hi, a simple solution might be the following small detour: first create entries with the same main entry (your subentry) and different subentries (your main entries). This is done by using the toolbar-> small triangle on the right: „clear levels after creating entry“. If you unhook this feature, the main entry will be kept, and you can quickly create entries with different subentries.
Finally, select all these entries in the index list and swap first and second levels using the index action „swap level“.