Having Sub Categories?

First of all, i want to say that i love this plugin, we use it to have people make appointments through our website for getting their phones and tablets repaired.

Even though we did link it per product/repair to have people plan an appointment on a product page, we do have the option on a seperate single page to be able to select from a category and a service to select a repair freely in this list.

The problem is though, for example, we do different repairs (apple, samsung,huawei etc)
Once you would select a brand in the first categories select box, say, we select Apple, then the list of services under that category is still a mess having to select something in a very long list between all different models and their repairs.

So my question is, is there a way to modify the plugin in such a way, that there is a second level of categories to choose from, or perhaps being able to filter between services that are in the selected list? Or perhaps there is a plugin that does this for us? This would ehance the plugin by so much!

Thanks in advance!