When you load a save, you will get a MuMech window. Press --Select-- and find the Impossible Innovations tech tree.
Just click on it, and you're done.

To install manually, just take the tree.cfg file in this directory and put it in the save 
folder you want to use it in. You still need TreeLoader.

--NOTICE--

You if you want to add/update the tech tree on an exsisting save, you need to manually install the new tree.
