Iconview icon selection appearance

I work on a project using Gtk & Ruby. I want when one icon was selected,
it shouldn’t seem as a rectangle.

http://i.imgur.com/RIEBipq.png

It just seem icon bound was selected. How can supply this?
http://i.imgur.com/LzT4H3C.png

I use iconview like below:

iconview = Gtk::IconView.new
file_store = Gtk::ListStore.new(String, String, TrueClass, Gdk::Pixbuf)
iconview.model = file_store
iconview.text_column = COL_DISPLAY_NAME
iconview.pixbuf_column = COL_PIXBUF

How can I code for this appearance?