6 ft tall, white flowers at top of shrub.
Just finished bloom.
SOLVED: Shrub I D
That's definitely a Spirea of some sort - Spiraea sp.
There are quite a few that could be commonly found in the Pittsburgh area.
Spiraea nipponica 'Snowmound' is quite often planted, and comports to the description you've provided thus far.
How about showing the whole plant, and additional detail images beyond the piece you collected?