What is the importance of trees for human beings?
Same advantages other animals get, plus we can get wood, resin and paper. They give us shade and fruits, their roots hold the soil so landslides become less common. Obviously, they eat and breathe what we don't, and turn what they eat and breathe into what we eat and breathe. CO2 into oxygen, and organic substances left by decomposition into leaves, flowers and fruits. Maybe we don't eat leaves and flowers, but some animals do, then we eat the animals. They aren't good for animals alone, they're also a great environment for fungi (mushrooms) that keep the soil clean, as they act as sponges which absorb heavy metals or toxic stuff.