where do i go after i finish the tree
Have you done the reverse tree and/or spent some time in Immersion? A lot of people do those. And then after they do the reverse tree, some people ladder from the language they just learned to another one! (For example, I would take Spanish for English speakers, then English for Spanish speakers, then German for Spanish speakers. ) Language is a lifelong journey. Get creative with it and don't stop! :D
There is no "place to go". You can try immersion or another language or simply keep on goldening your tree.
Anyways, Congrats on finishing it! :D
Start using the timed practice to go through the tree again. Exhaust all the material offered by Memrise and Anki. That will keep you busy for a long time.
If you are using the Chrome browser you can download their Language Immersion app which lets you adjust how much of any given web page you want translated into just about any language.
All of these suggestions are for a passive learning approach such as that offered by Duo.