I have a fairly large weeping cherry approx 10 years old 8' high by
12' wide that appears to be not healthy. I live in the NE USA NYC
area. The tree sits in full sun and in a 12' to 15" planted area next
to my driveway. The soil is not very drained, nugget mulched, and soil
is hard and clay like and some roots appear to making their way to the
surface.

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?