Code folding options are in preferences under Editor>Code Folding; however, (as far as I know) that only allows the entire if/else structure to be folded. Individual cases within it can't. At least that's the way it is in R2015b and R2019b. Anyone is free to prove me wrong on that.
EDIT: It may be of interest to point out that while individual cases within an if-else structure aren't foldable, cases within a switch-case structure are.