Hierarchy for Cases

A flat list of cases is not suitable to organize bigger projects.

Cases need to be broken down into smaller parts that are assigned to different people or teams.

In our projects we keep struggling to keep the number of cases low enough to not get lost and still have the individual case defined well enough to know what is about.

A hierarchy of case->sub-case->... would help a lot and is standard in other tools.

I am not talking about defining reference fields by ourselves. I am talking about built in functionality that can display cases as trees, just like it is possible with tasks.