  Recent studies of La$_3$Ni$_2$O$_7$ have identified a bilayer (2222)
structure and an unexpected alternating monolayer-trilayer (1313) structure,
both of which feature signatures of superconductivity near 80 K under high
pressures. Using angle-resolved photoemission spectroscopy, we measure the
electronic structure of 1313 samples. In contrast to the previously studied
2222 structure, we find that the 1313 structure hosts a flat band with a
markedly different binding energy, as well as an additional electron pocket and
band splittings. By comparison to local-density approximation calculations, we
find renormalizations of the Ni-$d_{z^2}$ and Ni-$d_{x^2-y^2}$ derived bands to
be about 5 to 7 and about 4 respectively, suggesting strong correlation
effects. These results reveal important differences in the electronic structure
brought about by the distinct structural motifs with the same stoichiometry.
Such differences may be relevant to the putative high temperature
superconductivity.
