Returns the completion tree for this instance.
        
        :return     <QTreeWidget>

def completerTree( self ):
        """
        Returns the completion tree for this instance.
        
        :return     <QTreeWidget>
        """
        if not self._completerTree:
            self._completerTree = QTreeWidget(self)
            self._completerTree.setWindowFlags(Qt.Popup)
            self._completerTree.setAlternatingRowColors( True )
            self._completerTree.installEventFilter(self)
            self._completerTree.itemClicked.connect( self.acceptCompletion )
            self._completerTree.setRootIsDecorated(False)
            self._completerTree.header().hide()
            
        return self._completerTree