I'll admit upfront I'm having trouble visualizing and recalling your configuration and how you've setup your system. So I'll provide a general answer, which hopefully with guide you forward.
For each of the Items To Show in Theater View (and we'll focus on just Video), there is a cascading sequence of configurations, such as Video > Shows > Series. The top-level items just selects the types of files that will be displayed in the view (the query). For Shows, it is Media Sub Type = TV Show.
But at the those bottom-level ltems, such as Series, there is one or more Details items. And these items tell MC how to group the resulting files (from the query). For Series, it is Series and Season. These are just MC fields, values you set (or MC auto-set), to distinguish one file from the next. MC collects all the like items at each of those levels (Series and Season) and presents them as groupings for you to select and drill down into.
So the question is... what "thing" do you want to use to cause a grouping? If the data is already in an MC field, you can add that field name somewhere under Details. Or, it could be an expression that calculates some value for each file (such as part of the file name or its path), and so an expression category can be added under Details.
Stated another way, if you select one file, and look at all the metadata for that file in the Tag Action Window (showing all values), which field, or part of which field, do you want to grab and use as the basis for creating some grouping?