"The basolia (Ukrainian: Басо́ля, Polish: basy or Polish: basetla) is a Ukrainian or Polish folk instrument of the bowed string family similar to the cello, although usually slightly larger and not as sophisticated in construction. The basolia was usually homemade and of very rough construction. Sometimes the soundboard was sewn to the body rather than glued. The strings are tuned in fifths."

I just copied the text from the english wiki page. The instrument was used by the Warsaw Village Band aka Kapela ze wsi Warszawa on their "People's Spring" releases.