I was about to explain that trees in AAA are almost always SpeedTree, but then I realised who was asking. 😋 So instead I'll ask: Do you have reason to suspect its not SpeedTree?
SpeedTree shaders in Unreal are pretty good, and it does a good job of generating billboards for you with good normals. I suspect there's nothing revolutionary about what they're doing, they've just spent a lot of time and resource on getting them as good as possible.
@Benjammin , yeah the speedtree standard stuff is not bad at all. I have been perfectly happy with it. Until I saw this game :). I am convinced that they have done a little extra with the shaders. It may just be a few simple tweaks but it is very different looking from the vanilla look you get. Well, it dawned on me to…