It looks really close to that tree. They want to tree to grow, so they make the wall more malleable in that section. If they did the regular wall all the way across, it would look horrible, and probably cause problems for a larger section of wall, when the tree roots start breaking it up on 10 years.
Or else they did do the wall all the way many years ago, but the tree already started breaking it, so they cut out that section.
It looks really close to that tree. They want to tree to grow, so they make the wall more malleable in that section. If they did the regular wall all the way across, it would look horrible, and probably cause problems for a larger section of wall, when the tree roots start breaking it up on 10 years.
Or else they did do the wall all the way many years ago, but the tree already started breaking it, so they cut out that section.