Adds the inputed item to the gantt widget.
        
        :param      item | <XGanttWidgetItem>

def addTopLevelItem(self, item):
        """
        Adds the inputed item to the gantt widget.
        
        :param      item | <XGanttWidgetItem>
        """
        vitem = item.viewItem()
        
        self.treeWidget().addTopLevelItem(item)
        self.viewWidget().scene().addItem(vitem)
        
        item._viewItem = weakref.ref(vitem)
        
        if self.updatesEnabled():
            try:
                item.sync(recursive=True)
            except AttributeError:
                pass