Comment by Abimelex

> People who can see at least three trees from their window have better mental health than those who can't. It seems like the easiest of the three goals to achieve

Here we go, correlation does not equal causation. Simple as that. Planting 3 trees will not give you a better mental health nor will planting 10 trees. But moving in to an environment where many trees grow in front of your window will probably change a lot more than just putting trees in your view.