Research shows its not necessary to add a tree preservative to the water for your Christmas tree, said Eric McConnell, forest product specialist with the Ohio State University Extension. It wont keep the tree fresh longer than plain water.
What is important is to never let the cut end get dry in the stand, because then it will seal over with resin and lose its ability to take up water, McConnell said. Slice about a half-inch off the bottom of the trunk just before putting it in the stand, and use a stand that can hold plenty of water. McConnell said the stand should contain one quart of water for each inch of trunk diameter, and you should always keep at least about a gallon of water in the stand.
Because the part of the tree that takes up water is just below the bark, dont trim the outside of the trunk to fit the tree into the stand.