Nested, crashing sidebars with Bootstrap, Scrollspy and Collapse?

I would like to create a sub-navigation sidebar navigation that appears when the user enters the parent section on the page:

eg https://parse.com/docs/ios_guide#queries/iOS

I think the way to do it using bootstrap is a combination of plugins affix

, scrollspy

and collapse

, but I'm not sure how to fire the correct event collapse

when the user scrolls or clicks on the correct parent section.