Collapse block in Selection screen

Hi

In Webdynpro i create a selection screen with block using IF_WD_SELECT_OPTIONS->ADD_BLOCK

  wd_this->m_handler->add_block(

     i_id         = `BL02`

     i_block_type = if_wd_select_options=>mc_block_type_tray

     i_title      = `Udvidede selektioner`  ).

But i would like to have the block Collapsed as default. How can i do that?