Create online bookings by category

It would be great to be able to create an online booking calendar by Category rather than just practitioner or appointment. For example a few of our therapists offer services in different massage categories, but at times we want to direct people to just one category. When you have multiple treatment times available in a category you want them to be able to book all of those times. At the moment if you choose practitioner then it shows all treatments across different categories, if you then choose appointment you get just one appointment rather than all of those available in that category.