30 Rock studio question

[Kevin Vahey]

Watching Sunday Night Football on NBC last night they were using the
studio that looks out on the rink as usual. However the tree was on
the other side of the rink and since the tree is directly in front of
30 Rock it makes me wonder where the studio is or how they pull off
the illusion. It appears to be a window given the foscus aspect on
some shots so it isn't rear screen as far as I can tell.