As the name already tells it is a "licht" (light). And it is only tagged as artwork, not monument or installation. Here is a picture of it: https://de.wikipedia.org/wiki/Leutschenpark#/media/Datei:Christopher_T_Hunziker_Leutschenlicht_Baumtopf.jpg. So it does no appear all of a sudden out of the bottom, but from the sky ;-)

Maybe it could be tagged as a line instead of a node.