The recycler breaks things up into the parts needed to make it. So if you stick a Worker in you'll get 4 planks, 4 poles and a Gear out. But if you stick a Plank in you get a Plank out because nothing was put together to make a Plank.
A full size tree is grown by planting a Seedling instead of a Tree Seed. Try putting Tree Seeds into the Seedling Tray.