The condition is that you have to have logged at least fifteen caches with the word "TREE" in the title.
To prove this just list the caches, by name or GC number in your log... OR better still create a list on your geocaching account page, it's easy!
The physical cache is at the posted coordinates. It has swag in it;- unusual for a TTM cache so bring your swag to trade. Trade up equal or better, no pillaging!
The difficulty rating reflects the work involved making the list. The physical cache is easy enough.