An example of minimal spanning tree of a directed graph. A directed graph consisting of four nodes, ’A’, ’B’, ’C’ and ’D’ is shown in the left hand side. Nodes in the directed graph are completely connected to each other with integer weights ranging from 1 to 12. In the right hand side, the corresponding minimal spanning tree of the directed graph is shown. The tree has the minimum total weight among all possible trees contained in the directed graph.