  In the framework of type II seesaw mechanism we propose two simple but
instructive ansatze for neutrino mixing and leptogenesis. In each ansatz, the
effective Majorana neutrino mass matrix is composed of two parts -- the part
with Z_2 symmetry arises from the ordinary type I seesaw mechanism and the part
with S_3 symmetry arises from an additional Higgs triplet vacuum expectation
value. The two ansatze can simultaneously account for the current neutrino
oscillation data and the cosmological baryon number asymmetry via leptogenesis.
