Research Areas and Research Topics
It may be necessary to build certain topics with a 2-level (how many levels make sense?) hierarchy.
Idea: Have a "Research Area" (wide and unspecific) and specialized sub-areas or "Research Topics" that deal with a more specific part in detail.
See https://writemd.rz.tuhh.de/VHkBiN0BSx2oQY_pYIpk9w?both for an example