Sprite is sugar, water and carbon dioxide. The sugar is like the nutrients that the roots have stored, and are sending into the canopy so the leaves have more energy to build more plant tissue. The CO2 out gases so fast it is useless. The water is critical to keeping the leaves moist through the season, when the roots have been cut.
Aquarium ferts (N, P, K, micros) are like the fertilizer that the roots pick up from the soil and send into the canopy so the leaves have the raw materials to build more plant tissue.
Excel is a carbon substitute for aquatic plants. Picked up via the leaf instead of CO2.
Since the goal of a cut tree is not to grow, but simply to stay moist enough not to be a fire hazard, I would skip any of the above, and just make sure plenty of water is available. If you have a live, potted tree that you will be placing in the garden, then the aquarium ferts would be best, but not much of them. Water is, again, the most needed thing.
I might be wrong; maybe there are studies showing that cut trees take in more water if there is an additive. More water = better fire resistance.
Every one that I google has the same advice for trees, wreaths, and similar greenery:
Fresh cut at the end. As little as 1/4" is enough, but it must be done. The channels that carry the water up get plugged while the tree is on the lot.
Keep the tree in water. If you are not bringing it in right away that is fine, but stand it in water while it is in your yard.
Keep the basin filled with water. Check often, trees can use a lot of water.
If you really want to use something, spray the tree with an antitranspirant such as WiltProof or Cloud Cover sort of product. These are sold in nurseries to help plants resist frost damage, or drying out from wind or from the shock of transplant. Read the label to be sure it is safe indoors. Do the actual spraying outside and wait until the tree, wreath or greenery is dry to bring it in. These are OK if you intend to compost the tree after the season, they break down pretty fast.
"If you want to make a Christmas tree last longer, just use plain water. Studies have shown that plain water will work as well to keep a Christmas tree alive as anything added to the water.
Check the Christmas tree stand twice a day as long as the tree is up. It is important that the stand stayed filled. A Christmas tree stand normally holds a rather small amount of water and a Christmas tree can quickly use up the water in the stand."
"Always keep the base of a tree in water. If the base dries out, resin will form over the cut end and the tree will not be able to absorb water and will dry out quickly. You don't need anything other than regular tap water - drying out deters future water uptake and will need a new cut. Commercially prepared mixes like aspirin, sugar and other additives introduce into the water are not necessary. Research has shown that plain water will keep a tree fresh."