speaking in terms of strict realism, the swaying trees seen in the myth 3 E3 interview are moving quite freely.
the movement of those large trees can only be duplicated in real life during a gale force hurricane which would not only break those trees eventually but without any doubt, send every single unit on the screen flying about like those flashing spots during a bad acid dream.
problem: tree trunks don't sway like rubber bands.
solution: make the trunks solid but the branches and the leaves able to sway slightly.
mb if someone is reading this, mb they can fix it mb.
-Welly