This is a fine place to discuss fine art! To me, it represents wind. I can feel it swaying that tall pine tree. Do whatever you want with your loins, Max, but you don't need to pull up your shorts. Au natural is a better way to make art.
I think it represents what Vincent actually saw. Don't forget that he was mentally ill. And many people with certain kinds of mental illness report that they sometimes see the world in this "swirly" fashion.