Answer:
90 branches
Explanation:
Since there are only 2 variables that might change the outcomes, we can simply multiply those variables by each other to get the number of outcomes.
15 * 6 = 90
To be more in depth with this...
For each flavor there would be 6 topping options, right?
So if there are 15 flavors, we would have 90 different combinations of ice cream.
There isn't a varying cone flavor or something else to change the outcome, which is why the tree diagram would stop after the topping part.