My tree leans, but it's always leaned — what should I do?

A trunk off vertical with the upper crown bent back toward straight up, so the tree reads as a shallow bow or J rather than a straight stick tipped over; thicker bulged wood on one side of the lower trunk; soil flat and undisturbed all the way around the base with turf grown right up to the flare on both sides. Now the opposite list, which is the one that matters: a straight trunk tipped as a whole unit, a crescent crack or a heaved mound of soil and turf on the side away from the lean, roots lifting out of the ground, or a lean that has visibly changed against a fixed reference like a fence line or downspout. Lean alone is a poor predictor of failure, and an old lean is often evidence of the opposite. A tree that leaned slowly over years has been laying reaction wood on the loaded side the whole time and thickening its root plate to match — it has already engineered around the load. What actually predicts uprooting is root-plate movement, and root-plate movement shows up in the ground, not in the trunk angle. That is why the soil around the base tells you more than the lean does.