  Magnetoresistivity \r{ho}xx and Hall resistivity \r{ho}xy in ultra high
magnetic fields up to 88T are measured down to 0.15K to clarify the multiband
electronic structure in high-quality single crystals of superconducting FeSe.
At low temperatures and high fields we observe quantum oscillations in both
resistivity and Hall effect, confirming the multiband Fermi surface with small
volumes. We propose a novel and independent approach to identify the sign of
corresponding cyclotron orbit in a compensated metal from magnetotransport
measurements. The observed significant differences in the relative amplitudes
of the quantum oscillations between the \r{ho}xx and \r{ho}xy components,
together with the positive sign of the high-field \r{ho}xy , reveal that the
largest pocket should correspond to the hole band. The low-field
magnetotransport data in the normal state suggest that, in addition to one hole
and one almost compensated electron bands, the orthorhombic phase of FeSe
exhibits an additional tiny electron pocket with a high mobility.
