These look like Jack-o-Lantern fungi, which unfortunately is a type of active wood decay. You might want to have the tree evaluated by a certified arborist, and it may need to be removed before it becomes a fall hazard, depending on what is nearby. (If falling would not damage anything and won't pose a risk to people, there is no need to remove the tree, as many wild animals benefit from dead/dying trees.)

The fungus entered the tree long before the mushrooms appeared (and similarly, tree decline can begin quite a while before symptoms manifest), and there is no way to cure the condition. Interestingly, these mushrooms glow in the dark, though you'd have to be sitting in a fairly dark room for long enough to adjust your eyes to be able to see their faint glow from the gills.

Miri