Ways to preserve Christmas trees??

my dad wants to get a real christmas tree for the holidays and he wanted to know ways to preserve it so that it wont die......he already has a fake one(and he wants a real one) so please dont answer that........he wants to try getting a real one and i know its dangerous but o well.......... my stepmom has heard of putting sprite in the water that the christmas tree sits in but she is not sure so if u would please tell me some ways to preserve the tree so that it will stay alive through Christmas please let me know!!!