The answer to 'why is my tree dead trees' is that there are several common causes for a tree to die, including disease, pests, environmental stress, or improper care. Common symptoms of a dead or dying tree include wilting leaves, peeling bark, sparse foliage, and a lack of new growth. To revive a dying tree, you'll need to identify and address the underlying issue, which may involve pruning, treating disease or pests, or improving soil and water conditions.
If the tree is beyond saving, it's best to have a professional arborist remove it safely to prevent damage or injury. Attempting to remove a large, dead tree yourself can be extremely dangerous.