  The origins of the stellar-mass black hole mergers discovered by LIGO/Virgo
are still unknown. Here we show that, if migration traps develop in the
\add{accretion} disks of Active Galactic Nuclei (AGNs) and promote the mergers
of their captive black holes, the majority of black holes within disks will
undergo hierarchical mergers---with one of the black holes being the remnant of
a previous merger. 40% of AGN-assisted mergers detected by LIGO/Virgo will
include a black hole with mass $\gtrsim 50$ M$_\odot$, the mass limit from
stellar core collapse. Hierarchical mergers at traps in AGNs will exhibit black
hole spins (anti-)aligned with the binary's orbital axis, a distinct property
from other hierarchical channels. Our results are suggestive, although not
definitive (with Odds ratio of $\sim 1$), that LIGO's heaviest merger so far,
GW170729, could have originated from this channel.
