Weeping willow - whole limbs breaking off
I have a 30 year old weeping willow, appeared healthy, in last 4 weeks tree has lost a huge limb plus a few other branches in 2 separate episodes. Inside of tree is now open, some insect damage visible. Location of tree is near edge of a pond which has had high water last couple of years, but tree is above water separated by a 20 year old retaining wall. Did not have high winds. What is causing this dramatic change and apparent death?