Custom menu meta box in admin=>appearance=>menus

I’m trying to create a custom meta box in the admin=>appearance=>menus page and have it’s items save in a menu, just like the other meta boxes (post/pages/categories/tags/links).

The wp api does not seem to make this easy. I’ve managed to create a custom meta box but I don’t know how to get it’s items to show up in a menu once “add to menu” is clicked.

if anyone could help me out I’d really appreciate it. I assume there is ajax involved but I can’t find where to do what.

Thanks.