It's not the trees. It's the females. Disgustingly off-topic, but... roots in plastic pipe? Maybe, but I've never seen it.
I'm suspecting some complicating factor, like a collapsed pipe or maybe some kind of calcification - a few years ago I caught some helpers I hired washing heavily encrusted drywall and paint tools in the sink... they might have been doing it for a week.
Anyway, every time I have a gaggle of females in the house, (AirBnB) no matter how explicit my lecture, I end up snaking tampons, "wipes," towels, etc. from that one spot. Very close to where the line from the garage meets the main line.
Now I threaten to mail any material I recover back to them. Of course, AirBnB doesn't actually give me their address, but they might not know that. Haha... I could maybe scope the sewer as part of the check-out procedure.