First of all, you have to know is "apple" a company name? If it is a company name then it comes with "s" or not? Using apostrophy here means possessive, so, if apple owns the group the correct answer is "apple's group. if the name is "apples" then you should use "apples' group".
You can always test the use of apostrophy by putting the expression into an "of" phrase. You'll then recongize the ownership word. So, if "the group of apple" is what you want to say then it should have apostrophy after apple = apple's.