Фильтровать select

var car_models = [ 
{'BMW':"X5"}, 
{'BMW':"X6"}, 
{'Mercedes':"Class C"}, 
{'Mercedes':"Class A"}, 
           ]; 
 
 
var $select1 = $( 'select[name=select_marka]' ), 
    $select2 = $( 'select[name=select_model]' ), 
    $options = $select2.find( 'option' ); 
 
$select1.on( 'change', function() { 
    var marka =  $(this).find(":selected").text(); 
    var model =  car_models.map(function(x){ if (x[marka]!='undefined') return x[marka]}); 
     
   
  $select2.html( $options.map(function () {  
   if (model.indexOf($(this).text())!=-1){ 
      return this; 
   } 
   
  })); 
 
} ).trigger('change');

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> 
 
<select name="select_marka"> 
<option>BMW</option> 
<option>Mercedes</option> 
</select> 
 
<select name="select_model"> 
<option>X5</option> 
<option>X6</option> 
<option>Class C</option> 
<option>Class A</option> 
<option>Class S</option> 
</select>