In planning view, where I can create a backlog item (top left drop done near "To be planned"):
- The drop down also propose the parent types of the accepted elements (eg. Epics of User Stories)
- The parent tracker type is proposed if
- it's outside the planning configuration (eg. Epic parent of user story but in planning config, only user stories are managed)
- it's type is accepted by the milestone (eg. Epic -> Release and US -> Sprint, in Release planning I can only see user stories but I can add Epics too because Releases accept Epics)
- In that case the Epic will be added directly to the Release
- it's accepted by the parent milestone (eg. Epic -> Release and US -> Sprint, in Sprint planning I can only see user stories but I can add Epics because the parent of the milestone accepts epic)
- In that case the Epic will be added to the parent milestone (the release)
Note: when a new element is added to a milestone, milestone ancestors are updated as well (eg. Themes -> Products, Epics -> Releases, Stories -> Sprint, When I add a new Epic from Sprint Planning, the epic is attached to the Release and the Product).