I made level 12.
Hi after a week of hard graft plodding through all the basic stuff again, I finally made level 12. However, I still see no further topics. Don't tell me I've been wasting my time! Where is the more advanced stuff?
If you mean you've finished the tree, you have a few different options at this point. You can do immersion (see immersion tab), you can do a reverse tree (i.e. studying English from Spanish), and/or you can review the lessons on the tree. Or, of course, if you think you've exhausted what Duolingo can do for you, you can move on to a different method of study.
As others have said, there is no advanced material other than what you see in the tree. The levels don't mean anything. They are just a measure of how many XP you have.
Your best bet probably is to do the Reverse Tree. (Study English as if you were a Spanish speaker.) That way you are totally immersed in Spanish, and interacting with others in the the Spanish-speaking discussions.