Trees in a field are usually found in clusters. So when and I see one I might stop suddenly to take a photo, hopefully without causing an accident.
In this case, I saw the tree and continued driving until I could safely make a U-turn and park along the highway. But if there are no cars nearby, I may just hit the breaks and back up along the curb. That's a bad idea if someone is in the car, but by myself, it works.
Lone trees are an easy subject. There are (pardon the pun) the low hanging fruit of landscape photography. Just find an angle that frames a solitary tree in its surroundings, and you have the makings of a good photo. In this case, I also have foreground and background elements that provide a sense of placement and perspective. And to top it off, no one was harmed in the making of this photo.