At the event level there exists a complex set of biological instructions ready to self execute when the proper conditions, such as good soil contact and appropriate soil moisture are met. Then it just grows, extracting nutrients from the land, water, and air. A cell divides here, a cell divides there. Day after day, year after year. It is an organic thing, fractal in nature, when a set of cells shoots off the main stem to grow into a branch. When many do so all at once at some very old injury it appears it happened at all at once. Life is full of branching.