Hi

after some tweaking I found answer for my question, here is one possible solution, it works only if categories are created from the scratch.

use strict;
use warnings;
use DBIx::Tree::NestedSet;
use DBI;
use Data::Dumper;

$Data::Dumper::Indent = 1;

my $dbh = DBI->connect('DBI:mysql:test','root','') 
                 or die ($DBI::errstr);
my $tree = DBIx::Tree::NestedSet->new(
                                    dbh        =>    $dbh,
                                    no_locking    =>    1,
                                    table_name    =>    'db_tree'
                                   );
$dbh->do("DELETE from db_tree");

#we can't have more "top" categories, so we create "main"
$tree->add_child_to_right( name=>'main' );

my %tree = ();

while (<DATA>) {
    chomp;
    my $hr;
    $hr->{last_node_id} = 0;
    my $t = \%tree;
    for my $item ( split '/' ) {
        #if path doesn't exists in hash
        unless ( exists $t->{$item} ) {
            #add to db
            $hr->{last_id} = $tree->add_child_to_right(
                name => $item, 
                id=>$hr->{last_node_id}
            );
            #make data hash structure
            $t->{$item} = { 'node_id' => $hr->{last_id} } ;
        } 
        $hr->{last_node_id} = $t->{$item}{node_id};
        print $hr->{last_node_id}, "\n";
        $t = \%{$t->{$item}};
    }
}

print "\n", Dumper(\%tree), "\n";

print "\nThe Complete Tree:\n";
print $tree->create_report();

__DATA__
foo/bar
bar/foo
foo/bar/foo
foo/bar/foo/bar/bar/foo
foo/bar/bar/bar
[download]

if the table categories is not created from scratch this will not work. So I have to find also answer to this question, anyone can help me :)