An Etymological Dictionary of the German Language/Zweig
Zweig, m., ‘branch, bough, twig,’ from the equiv. MidHG. zwîc (-ges), n. and m., OHG. zwîg, m.; corresponding to AS. twĭg, E. twig, Du. twijg; also in MidHG. and OHG. zwî (gen. zwîes), n. The g is probably evolved from j, and zwî, gen. zwĭges, may be traced back to a nom. zwîg. The AS. form twĭg is implied by the acc. plur. twĭgu (twiggu). Yet the primary forms cannot be ascertained with certainty, hence it is not quite clear how Zweig is connected with the numeral zwei (Zweig, Ut. ‘a division into two parts’?).