This tree recently failed and was cut down in my neighborhood. The picture shows the several branches just above the point on the trunk where they emerge ‘vertically’ crowding and growing tightly against one another, but separate with bark inbetween. The new lighter colored wood is no longer being added to their shared boundaries instead white mycellium is growing there consuming the old bark and creating space for rot to move further down into the trunk. The gaps can allow moisture and rot to penetrate. Wind can lever the limbs against one another causing a split to form down into the trunk.