title: ComboBox with two columns
body: <p>I'm trying to create a <code>GtkComboBox</code> with two columns. I picked up some examples and I'm trying to adapt but without success. Only the items that would be the second column are shown.</p>
  
  <pre><code>#!/usr/bin/env python3
  
  import gi
  gi.require_version('Gtk', '3.0')
  from gi.repository import Gtk
  
  class ComboBox(Gtk.Window):
      def __init__(self):
          Gtk.Window.__init__(self)
          self.set_title("ComboBox")
          self.set_default_size(150, -1)
          self.connect("destroy", Gtk.main_quit)
  
          slist = Gtk.ListStore(str, str)
          slist.append(['01', 'Ferro'])
          slist.append(['07', 'Uranio'])
          slist.append(['08', 'Cobalto'])
  
          combobox = Gtk.ComboBox()
          combobox.set_model(slist)
          combobox.set_active(0)
          combobox.set_wrap_width(2)
          self.add(combobox)
  
          cellrenderertext = Gtk.CellRendererText()
          combobox.pack_start(cellrenderertext, True)
          combobox.add_attribute(cellrenderertext, "text", 1)
  
  window = ComboBox()
  window.show_all()
  
  Gtk.main()
  </code></pre>
  
  <p>I want create a <code>GtkComboBox</code> like this:</p>
  
  <p><a href="https://i.stack.imgur.com/bJo1s.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bJo1s.gif" alt="enter image description here"></a></p>