Finder tag search exclusive

I am using tags to label all my documents in Finder, and Smart Folders to organise them, but I'm running into a roadblock. Lets say I have a bunch of documents with the tag "fruits", and some -- but not all -- documents also have additional tags like "apples", "oranges" etc. There is an unknown number of additional tags. I want to create a Smart Folder containing file that have only the fruits tag, and nothing else. How do you do such an exclusive search?