The trunk contains many vessels for transporting moisture and nutrients to the crown from the roots and manufactured food from the crown to the other parts of the tree. The crown is made up of branches, twigs, and leaves. This is the process of photosynthesis. The entire tree does not grow. The root tips grow deep into the soil and laterally out from the tree in search of more nutrients.
Roots provide support for the tree as it gets taller.
You can't really see this layer of cells between the bark and the wood, but it is what makes the tree increase in diameter. New wood cells are produced on the inside of the cambium layer and new bark cells on the outside of the cambium layer. This is why the bark of older trees is rough and furrowed or scaly. The old bark does not grow, so it has to crack and break apart as the new bark is produced beneath it. The buds are the other growth area of a tree.