  Exciton fine structure splitting in semiconductors reflects the underlying
symmetry of the crystal and quantum confinement. Since the latter factor
strongly enhances the exchange interaction, most work has focused on
nanostructures. Here, we report on the first observation of the bright exciton
fine structure splitting in a bulk semiconductor crystal, where the impact of
quantum confinement can be specifically excluded, giving access to the
intrinsic properties of the material. Detailed investigation of the exciton
photoluminescence and reflection spectra of a bulk methylammonium lead
tribromide single crystal reveals a zero magnetic field splitting as large as
$\sim 200\mu$eV. This result provides an important starting point for the
discussion of the origin of the large bright exciton fine structure observed in
perovskite nanocrystals.
