Get Sub Category List Of Particular Parent Category In Magento

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<select id="category" class="myinput-text required-entry widthinput" name="category">
<?php 
  $parentid=5; // parent id which you want sub category
  $categories=explode(',',Mage::getModel('catalog/category')->load($parentid)->getChildren());
  foreach($categories as $cat){ 
     $category=Mage::getModel('catalog/category')->load($cat);
?>
   <option value="<?php echo $category->getId();?>"><?php echo $category->getName();?></option>
<?php } ?>
</select>