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It is hard to diagnose a tree without seeing it. As a general rule, you can give it some balanced fertilizer and treat it with a pesticide and fungicide (I like neem oil as it is both in one spray). This should fix many issues it may have. If the tree still shows decline after these treatments, you will want to have a arborist come and take a look at it so they can better diagnose the issue.

You can try using a bolt split branch to the main trunk by installing long bolts through the trunk to pull the split back together and strengthen it. You can also install a cable through the branches above the split to prevent them from sagging and re-stressing the split. Any hardware you put in the tree will be eventually grown around and become a permanent part of the trunk.

A maple’s natural form is a rounded. Since they need very little pruning, you should only "train" for developing a leading shoot, which will eventually become the dominant shoot that establishes the tree's framework. Maples should not be pruned in spring and will bleed profusely if this is done. Therefore, it is best to wait to until late summer or early autumn to prune, and only on a young tree. You would typically not prune an older, overgrown tree unless absolutely necessary, and only then take off no more than a third of its growth within a given year.

What other symptoms are you seeing on the tree? Are the leaves yellowing? Are there any unusual things on the tree, like peeling bark, leaf spots, powdery substances? About how old is the tree? Let us know and we can better identify what is hurting the tree.

This article may help: https://www.gardeningknowhow.com/ornamental/trees/tgen/exposed-tree-roots.htm

Firewood is only a problem with ash trees. It is likely not the wood or the potting soil. What are the symptoms on the tree? Are there yellowing leaves, spots or other things? Any details you can give on how the branches go when they die will help us identify what is wrong with it.