just a thought can you betray ulfric stormcloak (i have no intention of doing it it was just a question).

.... sort of. You can go and give the Jagged Crown to Imperials to switch sides

Wen ya get da Jaggad crown ya can tek it to General Tullius an he let ya join da legion.
I have done it a few times.

You can, when get Jagged Crown, you can go and bring it to General Tullius, and join the Legion, and you can also to the same thing if you join the Legion first.

but how about after you gave the crown to ulfric??

No, before you do that, after, I think you can't.

Have you been at the Skooma Michael?

*looks left and right* ....Nope.

At a point late in the Main Quest (Season Unending) it was originally intended that you could betray and be cast out of your faction. A shame it didn't happen in the end.

The closest you can come is to do the peace talks and intentionally give your side a horrible deal

Those are pretty much the only ways you can betray Ulfric. You give the crown to Tullius and join the Legion, then, during 'Season Unending', make the terms wholly unfair for the Stormcloaks.