<select class="floatLabel" id="category" name="category" required="" data-parsley-errors-container="#category-errors" data-parsley-required-message="Это поле необходимо!">
      <option value="">
      </option>
        <?php foreach($categories as $cat): ?>
        <optgroup label="<?= $cat['name_rus']; ?>">

            <?php
            $query = $this->db->get_where('categories', array('parent_id' => $cat['id']));
            ?>
            <?php foreach($query->result() as $subcat): ?>
            <option value="<?= $subcat->id; ?>"><?= $subcat->name_rus; ?></option>
            <?php endforeach; ?>
        </optgroup>
        <?php endforeach; ?>
      </select>