  $\mathrm{Fe_{n=4,5}GeTe_2}$ exhibits quasi-two-dimensional properties as a
promising candidate for a near-room-temperature ferromagnet, which has
attracted great interest. In this work, we notice that the crystal lattice of
$\mathrm{Fe_{n=4,5}GeTe_2}$ can be approximately regarded as being stacked by
three bipartite crystal lattices. By combining the model Hamiltonians of
bipartite crystal lattices and first-principles calculations, we investigate
the electronic structure and the magnetism of $\mathrm{Fe_{n=4,5}GeTe_2}$. We
conclude that flat bands near the Fermi level originate from the bipartite
crystal lattices and that these flat bands are expected to lead to the
itinerant ferromagnetism in $\mathrm{Fe_{n=4,5}GeTe_2}$. Interestingly, we also
find that the magnetic moment of the Fe5 atom in $\mathrm{Fe_5 Ge Te_2}$ is
distinct from the other Fe atoms and is sensitive to the Coulomb interaction
$U$ and external pressure. These findings may be helpful to understand the
exotic magnetic behavior of $\mathrm{Fe_{n=4,5} Ge Te_2}$.
