  FeTe$_{0.55}$Se$_{0.45}$(FTS) occupies a special spot in modern condensed
matter physics at the intersections of electron correlation, topology, and
unconventional superconductivity. The bulk electronic structure of FTS is
predicted to be topologically nontrivial thanks to the band inversion between
the $d_{xz}$ and $p_z$ bands along $\Gamma$-$Z$. However, there remain debates
in both the authenticity of the Dirac surface states (DSS) and the experimental
deviations of band structure from the theoretical band inversion picture. Here
we resolve these debates through a comprehensive ARPES investigation. We first
observe a persistent DSS independent of $k_z$. Then, by comparing FTS with FeSe
which has no band inversion along $\Gamma$-$Z$, we identify the spectral weight
fingerprint of both the presence of the $p_z$ band and the inversion between
the $d_{xz}$ and $p_z$ bands. Furthermore, we propose a reconciling band
structure under the framework of a tight-binding model preserving crystal
symmetry. Our results highlight the significant influence of correlation on
modifying the band structure and make a strong case for the existence of
topological band structure in this unconventional superconductor.
