As someone that lives in an underserved community... the most impactful thing any billionaire could do is to just give the people living in these communities money directly.
Trees are one of those things we know have some impact on quality of life, whether they're mental health benefits from spending time in nature, or temperature impacts in urban areas (poorer neighborhoods have less vegetation, and therefore locally get hotter due to so called "heat islands")... but obviously people here don't care about trees because they're much further down on the hierarchy of needs than the wealthy. When you're worried about making rent you don't have time for trees.
So someone like Bezos sees a high-profile pat-on-the-back environmental project... which conveniently fulfills the "I know what you need better than you do" mentality that the wealthy generally hold over the poor... and tada! poor people get trees.