Here's a tree diagram that shows all the possible outcomes of tossing a coin three times:
```
T H
/ \ / \
T H T H
/ \ / \ / \ / \
T H T H T H T H
```
Each branch of the tree shows the outcome of one coin toss. For example, the branch on the far left represents the outcome TTT (tails on the first toss, tails on the second toss, and tails on the third toss).
To find the number of possible outcomes that could produce exactly 2 heads, we need to look for the branches that have exactly two H's. These are:
- TTH
- THT
- HTT
So there are three possible outcomes that could produce exactly 2 heads.