  We exhibit the simplex category $\Delta$ and Segal's category $\Gamma$ as
$\infty$-categorical localizations of the dendroidal categories $\Omega_\pi$
and $\Omega$ introduced by Moerdijk and Weiss. As an application we obtain an
equivalence of $\infty$-categories between invertible $\infty$-operads and the
$2$-Segal spaces of Dyckerhoff and Kapranov. Finally, we describe a cyclic
version of the dendroidal category and explain how it $\infty$-localizes to
Connes's cyclic category $\Lambda$.
