Dropdownlist from two tables data

I have two database tables; Sections and Categories.

Where Sections is:


----+----------

id  | name

----+----------

1   | fruits

----+----------

2   | flowers

----+----------

and tbl Categories is;


----------------+------------

id  | name      | section_id

----+-----------+------------

1   | apple     | 1

----+-----------+------------

2   | banana    | 1

----+---------- +------------

3   | rose      | 2

----+-----------+------------

4   | jasmine   | 2

----+---------- +------------

I want to create dropdownlist like this:


Select Category:

Fruits

  Apple

  Banana

Flowers

  Rose

  Jasmine

Where Sections items can’t be select.

I don’t have idea how create that with Chtml::dropDownlist.

Thank for help

Anyone please?