title: QTreeWidget how to add check boxes to children?
body: <p>I'm trying to add some check boxes to the children in a QTreeViewWidget, but they are not showing.</p>
  
  <pre><code>TreeList = ({
      'Header1': (('Item1', 'Item2', )),
      'Header2': (('Item1', 'Item2', )),
  })
  
  tree = QTreeWidget()
  
  for key, value in TreeList.items():
      parent = QTreeWidgetItem(tree, [key])
      for val in value:
          child = QTreeWidgetItem([val])
          child.setFlags(child.flags() | Qt.ItemIsUserCheckable)
          parent.addChild(child)
  </code></pre>
  
  <p>The TreeViewList populates as it should, but the checkboxes are not there, any ideas?</p>