Like humans, trees are able to grow in several different places at once. As a result, trees can simultaneously grow at the top from branches, at the bottom from their roots, and in diameter in the trunk.
For each area that trees are able to grow, they use a different method of growth. To elongate their branches, trees put out buds that eventually grow into leaves, branches or flowers. Each summer the tree forms buds for the following year. Because buds elongate branches, they increase both the height of the tree and the width of the canopy.
Like branches, roots also have several different types that grow in different directions. A tree has taproots, which enable the root system to grow straight down in direction. In addition it has lateral roots, which branch out sideways and increase the area of the root system.
Finally the tree can grow in the diameter of its trunk. It has four layers, the bark, a phloem, a cambium and an inner sapwood. The cambium is a microscopic layer that is responsible for adding new cells to the tree. The phloem is important because it brings nutrients from the leaves to the cambium, and the sapwood is important because it carries nutrients from the roots to the leaves.