CAKEPHP : Can use plugin in plugin?

example: I want use plugin tree in plugin forum I cant do this . Who can suggest about this ?

plugin in plugin , i mean:

Folder
App
----|plugin
-----------|plugin

If you talking about Plugin components or helpers, then yes. Plugin itself contain actions and you can call requestAction if you want to call exact action in another plugin.

About components and helpers do something:

class MypluginAppController extends AppController {
  var $helpers = array('Time', 'Otherplugin.Otherplugin');
  var $components = array('Otherplugin.Otherplugin');
}

In the Myplugin you can use Otherplugin (both component and helper) like

$this->Otherplugin->someaction();

Behaviours are working similarly, but you need to include them in myplugin_app_model.php