Question
Will winter freeze kill the aphids, and what damage will they do to the tree that is about ten years old.  and about 20 ft tall.

Answer
No the aphids will over winter in the bark crevices and will survive the cold. Next Spring as the new leaves are budding out treat the soil around the tree with a product called Bayer Advanced Tree and Shrub Insect control. This is a liquid and it is mixed in water. The amount will depend on the diameter of the tree trunk. Pour this mixture around the tree and the roots will take the insecticide up to the foliage and when the insects suck the plant juices they will be killed. This treatment should last all season. check with your local garden type store for this product or you can buy it on line form places like Do Your Own Pest Control http://www.domyownpestcontrol.com/