Leaf size shows something.
Is the UNION graft above ground ? Both ?!!
How many shoots are there - are they from the roots and not from the
graft - maybe you have Root Stock bush growing not the one that was
grafted above.
If there is a graft showing then the canes come from it or above it.
Below it is root stock of anything that has good roots. The Pretty is
grafted atop strong roots for a large plant and poor roots (by design)
in miniatures.
I don't have a degree in that subject but in other areas of Science.
Long time planter and viewer.
Martin