How can i save subcategory to my database in django

I am having trouble in saving subcategory data as it is dependent dropdown so in value i need to add category id but if i add category_id the subcategory having id of that category_id is being saved to my database for eg:- if my category id is 4 my subcategory having id 4 is being saved to my database.I think you will get clearance what i mean to say through my code... please check it once and help me resolve my issue...

    <form method="POST" action="" id="productForm" enctype='multipart/form-data'>
            {% csrf_token %}
            {{form.media}}
            {{form.media}}
            <p>Title:</p>
            {{form.title}}
            <p>Details:</p>
            {{form.details}}
            <p>Image:</p>
            {{form.image}}
            <p>Sp:</p>
            {{form.sp}}
            <p>Dp:</p>
            {{form.dp}}
            <p>Download Link:</p>
            {{form.download_link}}
            <p>Preview Link:</p>
            {{form.preview_link}}
            <p>Category:</p>
            <div class="col-xs-6">
                <select class="form-control" for="category" name="category" id="category">
                    {% for c in cat2 %}
                    <option value="{{c.id}}" for="category">{{c.name}}</option>
                    {% endfor %}
                </select>
              </div>
              <p>SubCategory:</p>
              <div class="col-xs-6">
                <select class="form-control" for="subcategory" name="subcategory" id="subcategory">
                    {% for i in adminsubcategory %}
                    <option value="{{i.category.id}}" for="subcategory">{{i.category_id}} {{i.id}} {{i.name}} {{i.category.name}}</option>
                      {% endfor %}
              </select>
              </div>
            <p>Tags:</p>
            {{form.tags}}
    <br>
            <input name="submit" id="submit" class="btn btn-danger" type="submit" value="Upload">
    
        
        </form>
    </div>
         </div>
        </div>
       <br>
       <br>
    
    <script>
    //Reference: https://jsfiddle.net/fwv18zo1/
    var $category = $( '#category' ),
        $subcategory = $( '#subcategory' ),
    $options = $subcategory.find( 'option' );
    
    $category.on( 'change', function() {
    $subcategory.html( $options.filter( '[value="' + this.value + '"]' ) );
    } ).trigger( 'change' );
    </script>