First of all: I replaced some "flying trees" next to the track.
I still have no clue, which trees stand around Suzuka, but with the new Acacia incoming, I tried that one replacing the oak and I have to say: it looks more natural and has a more pacific feeling to it - at least it fits better for Suzuka.
Nonetheless for all the oak lovers: Thanks to
Johnr777 I now know how to edit existing tree models (still have no clue about creating them). So I reworked the oak to make it look more natural. Simply go to the track-folder "rt_suzuka" --> extension --> trees and rename the "trees.txt" with the acacia to something else and rename the "trees_ReworkedOak.txt" to "trees.txt" to give it a try.
Feedback is always appreciated! Right now I'm not planning to work on Suzuka on my own anymore as everything seems fine for you guys. If you need a "better performance"-variant or have an idea about which trees to use in Suzuka, let me know! I'm on to my next track until then!