Trees are very, very good for our planet.
They are essential.
For one, they are great at carbon capture, working with symbiotic fungi.
Humans like looking at trees.
Native trees are best for wildlife.

There used to be many more trees covering the world.
Planting trees is cheap and easy
(often you can simply move saplings that have started growing in the wrong place;
or you can collect some of the many seeds that trees scatter in autumn and move them to where you'd like them to grow).
Please plant native trees! (Hedges count.)