  We study the orbital effect of a strong magnetic field parallel to the layers
on the energy spectrum of the Bernal-stacked graphene bilayer and multilayers,
including graphite. We consider the minimal model with the electron tunneling
between the nearest sites in the plane and out of the plane. Using the
semiclassical analytical approximation and exact numerical diagonalization, we
find that the energy spectrum consists of two domains. In the low- and
high-energy domains, the semiclassical electron orbits are closed and open, so
the spectra are discrete and continuous, correspondingly. The discrete energy
levels are the analogs of the Landau levels for the parallel magnetic field.
They can be detected experimentally using electron tunneling and optical
spectroscopy. In both domains, the electron wave functions are localized on a
finite number of graphene layers, so the results can be applied to graphene
multilayers of a finite thickness.
