How to present a select type(drop down) in a tree view format in Zend_Form

Question

Hello everyone, I am doing a new project in Zend and it needs a drop down which populates y the data from database (i.e Categories).I need to show those categories Data to be shown in the form of Tree view in the Drop Down menu.I have tried a bit doing it by just fetching the data from the database and then arranging them into the ZEND_FORM by using foreach and putting the value into the

$category->addMultiOption($childCategory['category_title'] , $childCategory['id']);

But still I am not getting the desired value in the Form.Please suggest how to do it because I am very raw in Zend Framework.A small code snippet will be very helpful to understand.

Thanks in advance.