We know there are two types of rendering of trees in this game. The full tree, for up-close rendering, and the simple tree with flat vertical branches for more distant rendering. Usually this works correctly but I've seen it many times, especially when in the middle of a forest, where the game isn't picking the render type correctly. Sometimes it seems that the game is using the vehicle-to-tree distance rather than camera-to-tree distance, with trees changing render type right in front of the camera. This is on the PC but consoles may have the same issue. See example below.
Here's the tree in full, when the vehicle is close but the camera is farther:
And here's the same tree in simple form when the vehicle is farther but the camera is actually closer: