Failing trunk began as a crack

This huge separation probably began as a crack in the branch union. It was preventable with appropriate pruning. An event such as a wind gust or simply gravity acting on the weight of the limbs may have caused the tree to finally split. This tree cannot be fixed and should be removed. This type of tree damage is not uncommon in urban landscapes. No one knows what percentage of trees eventually are removed due to structural defects such as this.