Of course, we already have trees in our ecosystem. If we were to gain more trees, then we need everybody to stop cutting them down for their gain. Nevertheless, we still need to use some trees to have mandatory everyday items. Trees partially need sunlight to grow and gain energy. With global warming gradually increasing, we may already have what we need to see trees continue to thrive. It is also helpful to plant trees ourselves; it is not a big difference, but it still helps.
There is also primary succession, this is the process of how trees grow. See more below.
Hope this basic outline helped, let me know if you need more info.