>>81912994 (OP)
It's autogynephilia AKA getting aroused when pretending to be a woman. So yes, it's a fetish. Mental illness also contribute but is not the main cause.
it's both, people can do the same thing for different reasons
I don't think it's a good idea to do it because of a fetish though (if you're MTF) because a lot of trans treatments kill your sex drive. Be careful.