I wonder if the proper translation of Gizrei Etzim is branches, as you wrote:
(Menachot 20b) One must bring at least two large branches - "veha'Goralos Hipalnu Al Korban ha'Etzim".
Perhaps a better translation would be "two large split and trimmed branches," since the branches were split and trimmed to size. See Kesef Mishneh to Rambam Temidim u'Musafim Perek 4.
b'Chavod Rav,
Zecharyah
Please note that in Review Questions and Answers we translated 'Gizrei Eitzim' as 'blocks of wood'.
Be'Virchas Kol Tuv
Eliezer Chrysler