Leonid & Friends, from Moscow.
From YT desc:
According to their Facebook page, Leonid Vorobyev decided to gather his musician friends to record one of his favorite cover tunes by the band, Chicago. The success of that one song led to seven more and the addition of even more musicians, which includes not just vocals, guitar, bass, drums, and keys, but a full horn section, violin, and flute.
Vorobyev claims it was a crazy idea.
Not so crazy. This band rocks. Check them out.