$ perl -MO=Concise,-tree t.pl
# from your code verbatim:
# ...
|-scope-+-ex-nextstate
|       `-ex-rv2sv---<4>gvsv(*bar)
`-<9>leave-+-<6>enter
           |-<7>nextstate(main 2 t.pl:11)
           `-ex-rv2sv---<8>gvsv(*baz)

# after adding warns
# ...
|-<i>leave-+-<c>enter
|          |-<5>nextstate(main 1 t.pl:7)
|          |-<7>warn[t1]---<6>pushmark
|          |-<8>nextstate(main 1 t.pl:8)
|          `-ex-rv2sv---<9>gvsv(*bar)
`-<i>leave-+-<c>enter
           |-<d>nextstate(main 2 t.pl:12)
           |-<f>warn[t2]---<e>pushmark
           |-<g>nextstate(main 2 t.pl:13)
           `-ex-rv2sv---<h>gvsv(*baz)