sub recurse {
    my ($ref, $car, @cdr) = @_;

    if ($prev_car eq $car) {
        my $hash = { name => $car, children => [] };
        push @$ref, $hash;

        return unless @cdr;
        $prev_car = $car;
        recurse($hash->{children}, @cdr);
    }

    push @$ref, { name => $car, children => [] };

    return unless @cdr;
    $prev_car = $car;
    recurse($ref, @cdr);
}