Even if you cut your tree youself, by the time you get it home, it needs to be recut across the bottom. It needs to go in water right after it's been cut, just like flowers do. We always cut off another couple inches before we put it in the stand, and then put some water in right away.
I had heard that putting a little bit of bleach in the water works and I did this a couple of years ago. I think it did work, but we didn't have a toddler and a dog then. I didn't do it last year because of ds2 and the puppy. This year, we also have a kitten, so there will be no bleach in the water again. But, if your kids are a little older and you've go no pets, then that is an idea.
I will try the sugar though.