How to simplify the filter

I´m working on the UI of the filter page that would allow the user to filter the Projects/Assets/Sub-assets to visualize the data. We are implementing a new "sub-asset" feature which will make the filter more complex. Right now we have two filter boxes - for projects. This fills up the box next to it called "case" with all the possible options of assets.

In the drawing below, I illustrated the updated version of the system - we are implementing the subassets where multiple subassets can have the same case. For this reason, the list in the filter box 2 is becoming longer and longer. Do you have any ideas on how to proceed with this to make the lists clear and short? I was thinking about implementing a new filter box next to it.