In a dense cities, the trees you see now that were allowed to grow to maturity were mostly likely planted by a human, with some exceptions of course. Any trees that began to grow organically were probably cut or eliminated.

>Trees definitely do not need us.

Until they do. Eventually bugs and diseases would kill off huge portions of them. Trees would still be around, but it'd definitely be a different mix than we have now. Right now every ash tree in my state is either dead or dying due to beetles, all the chestnuts died when I was a kid, the native oaks mostly only live where they've been planted because anytime one dies a faster growing maple replaces it.