我如何使用pyqt4将不同的背景颜色应用于树小部件中父文本的每一行

在我的示例代码中，我想为树小部件中的每一行的父文本应用不同的颜色，如何将背景颜色应用于父文本行，我尝试了Qbrush，但未获得预期的输出。有人请告诉我。先感谢您。

下面是我的示例代码：

from PyQt4 import QtCore, QtGui
class InventoryDelegate(QtGui.QStyledItemDelegate):
    def paint(self, painter, option, index):
        super(InventoryDelegate, self).paint(painter, option, index)
        if not index.parent().isValid():
            painter.save()
            painter.setPen(QtGui.QPen(QtGui.QColor("green")))
            r = QtCore.QRect(option.rect)
            r.adjust(0, 1, 0, -1)
            painter.drawLine(r.topLeft(), r.topRight())
            painter.drawLine(r.bottomLeft(), r.bottomRight())
            painter.restore()  
    def sizeHint(self, option, index):
        s = super(InventoryDelegate, self).sizeHint(option, index)
        s.setHeight(55)
        return s   
class Inventory_Items(QtGui.QMainWindow):
    def __init__(self, parent=None):
        super(Inventory_Items, self).__init__(parent)
        self.inventory_dict = {
            "Shirt": {
                "Formal Blue shirt": ["10.10.1(Red)", "10.10.2(blue)"],
                "Discount:0%": ["300", "400"],
                "Unit:Quantity": ["10", "5"]
            },
            "Frocks": {
                "Partywear Frock": ["10.10.1(pink)", "10.10.1(black)"],
                "Discount:0%": ["900", "1200"],
                "Unit:Quantity": ["50", "30"]
            }

        }
        self.inventory_widget = QtGui.QTreeWidget(columnCount=7,
            expandsOnDoubleClick=False,
            indentation=0,
            focusPolicy=QtCore.Qt.NoFocus,
            iconSize=QtCore.QSize(40,60))

        self.inventory_widget.setColumnWidth(2, 350)
        self.inventory_widget.setStyleSheet("QWidget {background-color: black;color: white;}")
        header = self.inventory_widget.header()
        header.hide()
        delegate = InventoryDelegate(self.inventory_widget)
        self.inventory_widget.setItemDelegate(delegate)

        for key, value in self.inventory_dict.items():
            icon = QtGui.QIcon("./{}.png".format(key))
            it = QtGui.QTreeWidgetItem()
            self.inventory_widget.addTopLevelItem(it)
            it.setIcon(0, icon)
            k = list(value.keys())
            for i, t in enumerate([key] + k):
                it.setText(i+1, t)

            e = [[] for _ in value[k[0]]]
            for k, v in value.items():
                for i, val in enumerate(v):
                    e[i].append(val)
            for r in e:
                child = QtGui.QTreeWidgetItem()
                for i, e_ in enumerate(r):
                    child.setText(i+2, e_)
                    it.addChild(child)
        self.inventory_widget.expandAll()
        self.setCentralWidget(self.inventory_widget)

if __name__ == '__main__':
    import sys
    app = QtGui.QApplication(sys.argv)
    settingobj= Inventory_Items()
    settingobj.showFullScreen()
    sys.exit(app.exec_())