How do I add extra paid content on Teachable?

Hi guys.

I'm making a course and hosting on Teachable. Haven't published yet, but I'm thinking of adding a second pricing tier with some extra lessons. I couldn't find any information on how to do this. Anyone know how?

The only thing I can think of is making a second course that includes the extra content. Should be easy, but I'd like learners to be able to upgrade directly from one to the other. I can achieve that by manually generating an upgrade discount code, but I'd like to eliminate that friction.