At the onset of spring, you will be able to unwrap the damaged tree and select a shoot or shoots, above the bud union, so as to renew your tree. Do not remove dead tree parts until new shoots are growing well. An even more effective insulation to preserve the bud union is a collar filled with sawdust to a point 6 to 12 inches above the union. The collar may be 5 or 6 inches in diameter. It is almost impossible to freeze tissue within this mass of sawdust.
Foliage is more difficult to save under severe frost conditions.
Any wrapping around and through it will help. Sometimes bunches of straw are intertwined with the foliage and matted around the branches to serve as an insulating mass. A suspended canvas and wood canopy above the tree will help. Under very extreme conditions, people have erected tents and placed lighted electric bulbs within the structure. Trees do not survive well in darkness, so the tree must be allowed to see sunlight during the day.