Turns out i'm too stupid for Octane.
index page says Octane 4 is here. decided to give it a try - downloaded demo - ta-dam - v3. no v4 available.
Looked through the forum - v4 is still in dev (and you can try it only by paying money) So what's the point of this "Octane 4 is here" if you can't try it ...

Speaking about archviz i don't get why you need to render all scene at once. All these trees can be (should be) added in post (so many great archviz companies do). There are plenty of real trees on the internet (royalty free, free...). Even if you need your 3d tree just render it alone with some ...