Could you please attach mocked up sample data as twbx ?
Here I have a simple way using Superstore data to replicate your use case.
1) I created a parameter using Sub-Category.
2) Then a Calc Field that calls the parameter,
3) Drag the calc field to filters shelf, show filter, and build the view like this and select "Show Relevant Values"
Would this work?
Note : Null is basically all product names that don't belong to the selected sub-category.