According to the PMBOK® Guide, specifically within the Perform Quantitative Risk Analysis process, a Decision Tree is a diagramming and calculation technique used to evaluate a situation in which a decision is faced and all the possible outcomes are not known with certainty.

Time Ordering: Decision trees are uniquely useful for showing the time ordering of events because they map out a sequence of decisions and their subsequent random events (risks) chronologically from left to right. Each branch represents a possible path or event that follows the previous one in time.

EMV Calculation: They are often used in conjunction with Expected Monetary Value (EMV) analysis to calculate the average outcome of multiple scenarios involving various costs and probabilities.

Analysis of Other Options:

A. Ishikawa (Cause and Effect): This diagram is used to identify potential root causes of a problem. It displays relationships between factors and an effect but does not illustrate a chronological sequence or time ordering of events.

B. Milestone: While a milestone chart shows significant points or events in a project over time, it is a scheduling tool rather than a " risk diagram " used for analyzing probabilistic outcomes.

C. Influence: An influence diagram is a graphical representation of situations showing causal influences, time ordering of events, and other relationships among variables and outcomes. However, within the specific context of PMI risk tools and the choices provided, the Decision Tree is the primary quantitative tool defined for evaluating sequential, time-ordered paths and their impacts.