I'd help them while laugh at the same time. In a good-hearted way though, because, come on, it's very funny, especially if they trip in a weird way. Unless they're hurt, so then of course I wouldn't laugh.
I'd help the person up and tell everybody to stop laughing at them. Especially if it was a really bad fall and the person who was tripped looks really upset.
I probably wouldn't even be there, because I'd be in the لائبریری XD But if I were, I'd help them up, and not bother with the people who are laughing. My teachers would deal with that.
