A tree is a subtype of graph. However, a DAG is not a tree if it has cycles once you forget direction, meaning paths can join up again after splitting. This dis

A tree is a subtype of graph. However, a DAG is not a tree if it has cycles once you forget direction, meaning paths can join up again after splitting. This distinction matters because when different paths "join up" again, there is often complicated data duplication/integration that is necessary in order order to combine the results. On a distributed system, it may mean data passing over a network, which you want to avoid.