Some thoughts:
One of the reasons I took up photography was to help my models be more accurate. Well, it worked enough to convince my wife..... I quickly found that perfection was an impossible goal and quickly settled on a "reasonable representation" frame of mind. Of course, I'm pretty arbitrary on my application of it.....
The best thing I can offer to anyone looking to do scenery (or even any model) is to study the real whatever. Yes, study trees. Stand back and look at them at all angles.
How are the limbs shaped?
Can you even see the limbs?
What's the overall proportion?
What makes one different from the one next to it?
How high are the lowest limbs?
How tall is it relative to other things like buildings, trains, telephone poles, etc?
Other details I like to consider:
how does it look at the ground? Does it flair a lot or just a bit or none at all?
How's the bark's texture? Color?
But most importantly, what will the model tree do on the layout? Will it be a scenic element all to itself or does it provide a representation or effect without being distractive to the real focus of the scene (usually the train)?
Obviously, my Live Oaks are "foreground" trees, meaning they don't blend in, at least I hope! They are planted in front of the tracks usually. For background trees like so many of us need in larger volumes, trees with no or little detail are more than suitable. They don't need lots of detail because they are behind the bulk of the scene, and the larger number of trees is used to manage an overall effect, not a single focal point.
It's not that one is better than the other, it's more about the purpose it serves on the layout.
