Update classtree.py

[(<type 'object'>, ()),                                                                                              
 [(<type 'exceptions.BaseException'>, (<type 'object'>,)),                                                           
  [(<type 'exceptions.Exception'>, (<type 'exceptions.BaseException'>,)),                                            
   [(<type 'exceptions.StandardError'>, (<type 'exceptions.Exception'>,)),                                           
    [(<type 'exceptions.EnvironmentError'>,                                                                          
      (<type 'exceptions.StandardError'>,)),                                                                         
     [(<type 'exceptions.OSError'>,                                                                                  
       (<type 'exceptions.EnvironmentError'>,))]]]]]]                                                                

object()
BaseException(object)
Exception(BaseException)
StandardError(Exception)
EnvironmentError(StandardError)
OSError(EnvironmentError)