For inspecting execution of installed makeinfo:

perl -d `which makeinfo` sample.texi

b  /usr/local/share/texinfo/Texinfo/Parser.pm:5344

p _print_tree ($current)

-----
For inspecting execution of Parsetexi module:

Uncomment DEBUG line in ./makeinfo.

b Parsetexi/lib/Parsetexi.pm:227

With _print_tree exported from Texinfo::Parser, can do

p Texinfo::Parser::_print_tree ($VAR1->{'contents'}[1])
