If you want vertical tabs with the ability to organize them in trees I suggest the Sideberry extension. It legitimately makes me nervous that the functionality would ever go away, it improves my productivity so much.
You can bookmark trees, collapse them, search them, load/unload them manually, I could go on. It makes it easy to organize dozens or hundreds of tabs. I have some trees for emails, news, forums, projects, etc. When I'm done just fold it up: the top tab bar can hide tabs that aren't in the active tree you're using, so you can still navigate the tabs normally.
Have you used it recently? Previous versions I would've agreed, but 5.0 was a huge improvement. If I didn't know, I'd likely have assumed it to be a native feature.
I'll take a look at Vivaldi's approach though, I've heard good things about those features previously.