Nice setup and rays. The tree trunks are a bit angular. You could try doubling polys in Poseray. Split the object in trunk and 'the rest', dump the rest (hide, delete hidden) and subdivdie the trunk, then go to import again, choose the object you just loaded again and hit 'merge'. The you have the trunk twice, but you delete the one from the initial object. Save (under different name). You have to go through the TG change to tgo again.