From https://github.com/keystonejs/keystone/issues/428

I don't think this has been implemented yet, and would like to see it done. Mainly, it would be nice to support nested pages and have a dropdown menu in the navbar. (The navbar in the live site, rather than the admin UI)

I've implemented something myself to allow one-level of dropdown menu. Where we currently compare key and section, I have added subkey and subsection fields, then edited the default template accordingly. My navLinks in middleware.js looks like this: http://pastebin.com/qgELHZuR

Happy to PR this implementation (which you can see live here: https://www.students4students.org.uk/), but it's perhaps a little too simplistic?