sub treebuilder {
    my ($filename, $level) = @_;

    my $PRESENTLEVELFILE;
    unless(open($PRESENTLEVELFILE, '<', $filename)) {
        warn "$filename: $!";
        return;
    }

    my $leafline = <$PRESENTLEVELFILE>;
    print $final "0 $leafline" if ( $filename eq $rootfile );

    while ( my $leafline = <$PRESENTLEVELFILE> ) {
        print $final "$level $leafline";
        my @element = split( '§', $leafline );
        treebuilder("$folder_IN/${level}_$element[0].CSV",$level + 1);
    }
    close($PRESENTLEVELFILE);
}