Trees are outdated technology that break to easy. A circ is a much more stable perc than a tree. Plus you get Wayyy more diffusion with a circ. That's why the major scientific glass companies dropped trees from the lineup.
US tubes makes a really nice UFO perc that hits better than any tree, less drag for sure and a little less splash with more bubblers. Both great pipes but the UFO is just a bit better IMHO> My buddy has this US Tubes UFO perc one and I have used it.