My father grew up in Squirrel Hill during the Depression. He celebrated his bar mitzva at Tree of Life in 1940.
I lived in Squirrel Hill during 1998-2000 while studying at Pitt. I belonged to Dor Hadash, which rents space from Tree of Life. Dor Hadash is a member-led congregation, although they have a wonderful female rabbi/cantor who leads some of the services. They are Reconstructionists, like to sing, and (mostly) politically liberal. Sounds like Makom to you?