If you open the hamburger menu and go to "more maps", you can click an info button next to the tree marker, which shows a popup with the word "Stadtbäume" (city

If you open the hamburger menu and go to "more maps", you can click an info button next to the tree marker, which shows a popup with the word "Stadtbäume" (city trees) which links to here: https://www.stadt-zuerich.ch/ted/de/index/gsz/natur-erleben/stadtbaeume.html https://www.stadt-zuerich.ch/ted/de/index/gsz/natur-erleben/... That page clarifies that these trees are indeed just the trees on public land, which are maintained by the city. Trees in private areas aren't included.