The treatments are represented in a tree diagram. Developing a tree diagram directs concentration from generalities to specifics. The event tree diagram models all possible pathways from the initiating event. A tree diagram is a connected forest diagram. Such a tree diagram is also called a phrase marker. Hence, the subsets can be represented using a tree diagram, or dendrogram. The resulting tree diagram is called a "deep structure". Tree diagram (7b) illustrates this structure with an example from English. The MCTS consists of a tree diagram in which the AI essentially plays tic-tac-toe. Take, for instance, the following tree diagram for example (4b). In probability theory, a tree diagram may be used to represent a probability space. A rooted tree diagram indicates the hypothetical common ancestor, or ancestral lineage, of the tree.