Make some options in a select menu “unselectable”

Question

I have a select element with a few options, but I want some of the options to not be selectable.

Basically it\'s like this:

Answer 1

jsFiddle Demo

You would use an

 
  City 1 Branch A
  City 1 Branch B
  City 1 Branch C
  
 
  City 2 Branch A
  City 2 Branch B