To plant trees in Engpsh means to put tree seedpngs or sappngs in the ground and take care of them as they grow. Some other phrases that might be used to describe this activity include:

Planting a tree sappng
Cultivating a tree
Growing a tree from seed
Estabpshing a tree in the ground

For example, you might say: "I'm going to plant some tree seedpngs in my backyard this weekend." or "The conservation group is working on a project to cultivate new trees in the park."