Answer: It is still early in case the tree can manage to try again to leaf out at the top, although any truly dead branches (no sign of a green layer just within the bark) can be removed. Unfortunately, some varieties of Japanese Maple really prefer partial shade and a sheltered location out of wind, so it is possible your site is not the best for this particular tree. To help it along, make sure it is watered regularly and mulched for this growing season as well. You might want to consult with the nursery where you purchased the tree (certainly if it is still under a guarantee) especially if the tree is grafted and the lower leaves are below the graft signalling a definite problem.
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