This bush is quite large compared to what I've seen when I googled for Isopyrum biternatum. The bush is about 3 ft tall and wide, and the leaves look larger. Mind you there wasn't too many photos that I could find and the ones I did showed mostly the bloom. It's amazing how many sites don't show photos of plants only descriptions.
Especially when trying to sort out closely similar plants photos may provide leads to what a plant may be but the information spelled out in descriptions will cinch it. Important deciding factors may not be apparent or noticed when using pictures only. Some plant manuals are nearly or completely unillustrated.
The photo of our flowers was taken on 22 April. Yours have also flowered and been fertilised, they already have small berries.Lucky you, we are still trying to get ours to set fruit! Praps our climate is not right .