Legal Question in Real Estate Law in California

Well, yes and no. Technically, overhanging tree and bush limbs and under-running roots are trespassory and the neighbor whose property is invaded thereby can seek a remedy, which is a step below being "required" to trim them in the sense you are required to stop at a red light.

Oftentimes, the offended neighbor uses the self-help remedy and prunes them himself, which is permissible. The neighbor is not entitled to be reimbursed for the cost of using a for-hire tree trimmer, however.

Judges don't want to hear suits between neighbors over trespassing vegetation, especially if no harm is being done (limbs contacting a structure, roots buckling pavement, etc.), so the best remedy is for the bush owner to admit fault and then discuss who will do the trimming.