Unfortunately I’ve drawn the same conclusion. Looking at the documentation for EKReminder - https://developer.apple.com/documentation/eventkit/ekreminder and EKCalendarItem - https://developer.apple.com/documentation/eventkit/ekcalendaritem, there is indeed no property for nesting calendar items... I also thought to check the EKCalendar - https://developer.apple.com/documentation/eventkit/ekcalendar class as this post - https://developer.apple.com/forums/thread/81097?answerId=266686022#266686022 made it clear that reminders lists are in fact EKCalendar objects. my hope was that this class would contain a map of some sort, but no luck. Ideally, EKReminder would be updated to contain a public property of type EKReminder[]... or something to that effect.