Twinmotion seems to have a region set for rendering trees. Outside that area, the density of trees decreases. You can see a line showing the difference in forest density.
Considering this phenomenon, instead of creating actual terrain, it is necessary to create terrain with the size of a real-world miniature model and disguise the forest using the bushes as trees in Twinmotion.
In that case, it is necessary to configure all characters and buildings in miniature size. It is necessary to use one model set for distant view and the other model set for close view. (Like a real miniature shoot.)
Twinmotion forest test