You missed to call ->eof.

use strict;
use warnings;
use HTML::TreeBuilder;

my $treeroot = HTML::TreeBuilder->new;
#$treeroot->store_comments(1);

my $whole_file = 'Some text. Some more text.';
$treeroot->parse( $whole_file );
$treeroot->eof();
#$treeroot->elementify(); # elementify doesn't matter either way.
$treeroot->dump();
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