 A rooted tree may be directed, called a directed rooted tree, either making all its edges point away from the root—in which case it is called an arborescence or out-tree—or making all its edges point towards the root—in which case it is called an anti-arborescence or in-tree.A rooted tree itself has been defined by some authors as a directed graph.A rooted forest is a disjoint union of rooted trees.