Represent a multi-stage finite sample space

A finite experiment has 2 stages. The stage choices are independent

At the first stage, the possible outcomes are green, blue. Their branch probabilities are \(\text{green}: \frac{1}{2}\), \(\text{blue}: \frac{1}{2}\)

At the second stage, the possible outcomes are green, blue. Their branch probabilities are \(\text{green}: \frac{1}{2}\), \(\text{blue}: \frac{1}{2}\)

Let \(S\) be the sample space of ordered stage outcomes

Let \(E\) be the event that exactly one stage outcome is green