In the summer, the green chlorophyll packages are very, very busy. The green packages in the leaves catch sunlight and, using it for energy, they change water from the ground and a special gas from the air ("carbon dioxide") into sugar ("glucose").
This sugar is the food for the tree.
All summer long the green chlorophyll produces food for the trees. Because the green chlorophyll is so busy, the green color covers up all of the other colors in the packages.