How much time has passed since you submitted your sitemap to Bing?
I am not sure about other SEO specialists, but I don't spend my time on Bing/Yahoo. As far as I know they have less than 30% of the search market together. I would rather allocate my time on moving more pages of my website to the 1st page of Google.
If you are still concerned about being indexed on Bing try to compare your website with your competitors (who are on Bing of course).
- See how many pages they have indexed.
- See if you can get the same backlinks.
- See what robots.txt they have. (Maybe the problem is in it.)
- See if your site has any errors.
- See if your site is banned from Bing for some reason.
The underscored points are those I would check first.
Warmest regards,
Slava