For the past two springs I have pruned this over the years to keep the weeping growth more like an umbrella shape. I may have over-cut a branch or two that was more like one of the main branches rather than shoots. Last spring, the tree blossomed but not as full or robust as usual. This spring same thing. Last late spring & summer the leaves appeared not robust with 25% dead branches. I suspect this year same thing after bloom. There's no question the tree is much alive but just unheathy looking based on earlier years.
I noticed at the crown where all the main branches stem from there to be a hard bulge not too normal looking with a gap in the center. The size of the main trunk is about 7" to 8" inches. It appeared last summer there were very small ants traveling in and out the crown and into the tree.
I want to understand what this growth could be and why/how insects penetrated it. I want to save it and seal that gap to stop the insect penetration. Can you give advise on what this can be - disease or stress, how to treat it, and how to seal the gap (what material / where to get). Also, am I doing all the right things to keep it healthy?