Unfortunately we aren't able to determine a diagnosis from the photos and this stage of advanced decline, but we do recommend that you consult a certified arborist or licensed tree expert, who may be able to narrow-down a diagnosis from an in-person assessment. Tree decline sometimes takes months or years after an injury or stress event to cause overt symptoms of decline, so diagnosis is sometimes difficult if the original symptoms of decline have since been obscured. While arborists can't cure every ailment or reverse decline, they can look for sources of tree stress so that this tree, nearby trees, or a replacement tree experience minimal stress going forward.

Miri