Look carefully at a tree. Trees grow from the top, so once a branch forms, it will never move any higher. Then shouldn't you still be able to see the branches that formed when the tree was only a foot high? As the tree grows, the lower branches are often shaded by the leaves of the upper branches. This causes the lower branches to die, and eventually break off. The tree continues to grow bigger, until the remains of the old branches have been enclosed by new growth. The star pattern was formed by the remains of branches from when the tree was young.