Legal Question in Real Estate Law in California

The first thing to do is stop assuming and find out who owns it. It sounds like you are in unincorporated county, which means it is very likely that your property line extends to the middle of the street, with an easment reserved for public access and byway, but you need to make sure. Next, you need to find out if the county considers it "their" tree. Many median trees were not planted by the public authorities and they claim no ownership or responsiblity for them. If it is on county land, and/or they claim ownership of it, take the issue up with public works. See if they will OK removing and replacing it with something more suitable. Chances are they will work with you.