use warnings;
use strict;
use XML::LibXML;

my $dom = XML::LibXML->load_xml({ location => '11117492.xml' });

# Build the tree
my (%nodes,%tree);
for my $part ($dom->findnodes('/products/product')) {
	for my $categories ($part->findnodes('./categories/category')) {
		my $cat_name = $categories->findvalue("name");
		my $cat_id = $categories->findvalue("category_id");
		my $cat_parent_id = $categories->findvalue("parent_id");
		$nodes{$cat_id}{id} = $cat_id;
		$nodes{$cat_id}{name} = $cat_name;
		if ( length $cat_parent_id ) {
			push @{$nodes{$cat_parent_id}{children}}, $nodes{$cat_id};
		}
		else { $tree{$cat_id} = $nodes{$cat_id} } # root node
	}
}

use Data::Dump; dd \%tree; # Debug

# Walk the tree to find leaves
my @queue = values %tree;
while ( @queue ) {
	my $elem = shift @queue;
	if ( $elem->{children} ) {
		push @queue, @{$elem->{children}};
	}
	else {
		print $elem->{name}," (",$elem->{id},")\n";
	}
}

##</code><code>##

{
  443026 => {
    children => [
      {
        children => [{ id => 445720, name => "Carrot" }],
        id => 443120,
        name => "Vegetables",
      },
    ],
    id => 443026,
    name => "Food",
  },
}
Carrot (445720)