If the plant seems to be an "official" plant--in a formal planting, or one of many of the same kind along a street--I would start by telephoning a real person at the Department of Public Works.
If that exact name isn't available, maybe Department of Parks? Maintenance? The underlying idea is "the guys/gals from the city with the big trucks and the power tools." School districts have divisions named "Buildings and Grounds," but cities rarely do; that's the kind of concept we're looking for.
In my little burg (approx. 35,000 people), if there isn't a tree out by the street--maybe the old one died or there just never was a tree--and a resident wants to plant a tree out by the street, s/he contacts the Department of Parks & Recreation for...get this!...a *permit
No permit needed to plant a tree in the yard, though, which is how the people who originally owned this house saddled future owners like us with a gigantic
redwood in the back yard, but if you want to put a beautiful gingko or other tree out between the sidewalk and the street, you need a $250 permit.
Oh, yes: AND the tree must be listed on the Approved Trees list for the City of El Cerrito.
Needless to say, we have not planted a tree out by the street. $250 plus upkeep of a tree seems a little steep, ya know?
But maybe you'll have better luck!
Sunset Zone 17, USDA Zone 9