Here is an interesting tree we recently removed in Webster, MA. The owner was concerned about the large split that had propagated up the lower trunk in the photo below.
The pronounced swelling at the base of the tree caught my attention. This is often a sign of a root rot progressing up into the lower trunk. The tree “senses” the weakness in its trunk and adds extra growth to that area to shore itself up. You can see in the photo of the overturned stump after we cut the tree down, where the root rot has decayed the center of the tree and where the tree added new sound wood around the perimeter of the stump in an attempt to preserve itself. Unfortunately, the decay had progressed about ten feet up into the trunk, leading to the crack opening up in a wind event, requiring the removal of the tree.