You want to get a Christmas tree that will last you the whole month, but it can be difficult to tell how "alive" trees are once they're on the lot. This Old House suggests grabbing a branch and gently pulling it towards yourself. The fewer needles that come off in your hand, the fresher your tree is.
For a second test, crush the needles between your fingers and smell them. If you can't smell that signature Christmas tree scent, move on to another tree. For more tips on how to pick a great tree, check out the full post linked below.
How to Pick the Perfect Christmas Tree [This Old House]