Is there a way to make a feat like Tough but that only gives the HP bonus to a specific class?

I want to make the the Monks have a the equivalent of a d10 Hit die and the easiest way to do that would be a +1 to HP. That I can do easily.

The problem is if the character multiclasses, they'll still get the +1 HP. Is there a way to limit it to one class?

So, setting a class prerequisite to Monk isn't enough as it counts Character levels and not class levels?

Edit: Answer by "Demystifying Homebrew" It is overall level not class level, sadly.

You would have to make it as a subclass feature for a homebrewed copy of their specific subclass.