Tree walking is definitely a local thing. In practice it only happens with a plot marshal there to guide it - it requires plot approval and plot supervision, and any of the players who can do it tend to save it for situations where it makes sense (this guy jumped into a tree, I'm gonna try to follow him) or with prior approval (hey Alexander, do I know the trees well enough on each end to guide a group through the trees, or should I find another way?). It also has the IG consequences of damaging the trees on either end of the travel, which obviously Dryads aren't super fond of.