No, work experience is not compulsory, yes there's no denial that people with work experiences do have an advantage over those who do not have any experience.

Having said that, your good academic performance throughout graduation in addition with good entrance marks including doing well in PI, essay writing etc can definitely fetch you seat in top B-School.

If you have already taken decision to go straight into MBA after BCom, then work in all these areas, since thinking about no work experience will not bring any positive results.Also, it's not that every individual who gets into top B-School has work experience with them, there are definitely exception.

Right now, your priority should be to focus on your studies, maintaining good scores constantly, and you may take up internships as well related to your area of study, not only will you learn but the certificate too will matter in the long run. It'll add extra points in your cv definitely.