Trees need to be inspected periodically by a tree professional for health and potential hazards.
Call right away if you see one of these warning signs:
Splits or cracks in the truck - indicates weakness and may be solved by bracing or cabling
Hanging branches - need to be removed before becoming a danger, consider the height and size before attempting to prune yourself. Do not attempt tree pruning from a ladder, contact a professional.
Tilting - can indicate a root problem.
Hollows, mushrooms - can indicate diseased, rotting or dying trees.
When it comes to safety, it's better to be over cautious.