// get your locations
$locations = ['Berlin', 'Hamburg', 'Stuttgart', 'Hannover', 'Heidelberg', 'Bern' ...];

// make them into collection if not already
$locations_coll = Collection::make($locations);

// chunk the database insert if there are too many records in the collection
$locations_coll->chunk(500)->each(function($chunk) {

    $inserts = '';
    // loop through locations
    foreach($chunk as $location1) {
        foreach($chunk as $location2) {

            // if locations are the same then skip
            if($location1==$location2) continue;

            // add to bulk inserts
            $inserts .= '(' . $location1 . '-' . $location2 . '), ' . PHP_EOL;
        }
    }

    // do the bulk insert
    try {
        DB::insert("INSERT INTO your_table (`locations`) VALUES $inserts");
    } catch (Exception $e) {
        print_r([$e->getMessage()]);
    }
});