from PyQt5.QtWidgets import QApplication, QWidget, QLabel, QTextEdit, QPushButton, QTreeWidget
from PyQt5.QtWidgets import QHBoxLayout, QVBoxLayout
from PyQt5.QtWidgets import QTreeView
from PyQt5.QtWidgets import QMenu, QAction
from PyQt5.QtGui import QStandardItemModel, QStandardItem
from PyQt5.QtCore import Qt, QPoint
import sys
__author__ = 'Moon_'
class TreeView(QTreeView):
    currentitem = None     # Здесь сохраняю выбранный item(modelindex) после обработки события от мыши
                                     # заново присваиваю None
    def __init__(self):
        QTreeView.__init__(self)
        self.pressed.connect(self.presseditem)
    def mousePressEvent(self, qmouseevent):
        QTreeView.mousePressEvent(self, qmouseevent)
        bt = qmouseevent.button()
        if bt == 2:
            if not self.currentitem == None:
                menu = QMenu(self)
                straction = 'Ok'
                action1 = menu.addAction(straction)
                action1.triggered.connect(self.action)
                point = QPoint(qmouseevent.globalX(), qmouseevent.globalY())
                menu.popup(point)
        self.currentitem = None
    def action(self):
        print('action')
    def presseditem(self, modelindex):
        self.currentitem = modelindex
if __name__ == '__main__':
    app = QApplication(sys.argv)
    widget = QWidget()
    widget.resize(200, 200)
    treeview = TreeView()
    layout = QVBoxLayout()
    layout.addWidget(treeview)
    widget.setLayout(layout)
    model = QStandardItemModel()
    model.setHorizontalHeaderLabels(['Форма',])
    item0 = QStandardItem('проба')
    itemroot = model.invisibleRootItem()
    itemroot.appendRow(item0)
    item1 = QStandardItem('проба1')
    item2 = QStandardItem('проба2')
    item3 = QStandardItem('проба3')
    item0.appendRows([item1, item2, item3])
    treeview.setModel(model)
    widget.show()
    sys.exit(app.exec_())