How can I save the file in TreeView as a json file

I can show and edit a json file in QTreeWidget form. How can I save this edited json file again on desktop.

my goal is to create a json editor that we can edit

import json
from PyQt5.QtWidgets import *
from PyQt5.QtCore import Qt

class ViewTree(QTreeWidget):
    def __init__(self, value):

        super().__init__()
        def fill_item(item, value):
            def new_item(parent, text, val=None):
                child = QTreeWidgetItem([text])
                child.setFlags(child.flags() | Qt.ItemIsEditable)
                fill_item(child, val)
                parent.addChild(child)
                child.setExpanded(True)
            if value is None: return
            elif isinstance(value, dict):
                for key, val in sorted(value.items()):
                    new_item(item, str(key), val)
            elif isinstance(value, (list, tuple)):
                for val in value:
                    text = (str(val) if not isinstance(val, (dict, list, tuple))
                            else '[%s]' % type(val).__name__)
                    new_item(item, text, val)
            else:
                new_item(item, str(value))

        fill_item(self.invisibleRootItem(), value)



if __name__ == '__main__':

    app = QApplication([])


    fname = QFileDialog.getOpenFileName()
    json_file=open(fname[0],"r")
    file=json.load(json_file)


    window = ViewTree(file)
    window.setGeometry(300, 100, 900, 600)
    window.show()
    app.exec_()

Okay I did not have a Json File handy to test this with but I took your code and transformed it some. Now you are dealing with a JsonTable along with your TreeWidget when you make any changes in your TreeWidget you simply update your JsonTable with those changes. This code is not complete and you will still have to render some of the sections on your own but it should give you a solid template to build from as well as a few nifty features you might not have been aware of ;)

import json
import argparse

from sys import exit as sysExit

from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QApplication, QMainWindow, QTreeWidget, QFileDialog, QDockWidget, QAction

class MenuToolBar(QDockWidget):
    def __init__(self, MainWin):
        QDockWidget.__init__(self)
        self.MainWin = MainWin
        self.MainMenu = MainWin.menuBar()

        self.MenuActRef = {'OpnJsonAct':0,
                           'SavJsonAct':0}

        # ******* Create the File Menu *******
        self.FileMenu  = self.MainMenu.addMenu('File')

        # ******* Create File Menu Items *******
#        self.OpnJsonAct = QAction(QIcon('Images/open.ico'), '&Open', self)
        self.OpnJsonAct = QAction('&Open', self)
        self.OpnJsonAct.setShortcut("Ctrl+O")
        self.OpnJsonAct.setStatusTip('Open an Existing Json File')
        self.OpnJsonAct.triggered.connect(self.GetJsonFile)
        self.MenuActRef['OpnJsonAct'] = self.OpnJsonAct

#        self.SavJsonAct = QAction(QIcon('Images/save.ico'), '&Save', self)
        self.SavJsonAct = QAction('&Save', self)
        self.SavJsonAct.setShortcut("Ctrl+S")
        self.SavJsonAct.setStatusTip('Open an Existing Json File')
        self.SavJsonAct.triggered.connect(self.SaveJsonFile)
        self.MenuActRef['SavJsonAct'] = self.SavJsonAct

        # ******* Setup the File Menu *******
        self.FileMenu.addAction(self.OpnJsonAct)
        self.FileMenu.addSeparator()
        self.FileMenu.addAction(self.SavJsonAct)

    def GetJsonFile(self):
        self.MainWin.OpenFile()

    def SaveJsonFile(self):
        self.MainWin.SaveFile()

class ViewTree(QTreeWidget):
    def __init__(self, parent):
        QTreeWidget.__init__(self)

        self.MyParent = parent
        self.TreeRoot = self.invisibleRootItem()

   # Just to show you what a static method looks like
   # one that does not need a reference to self because
   # it does not use self -- non-essential you can 
   # delete this when you are done testing with it
    @staticmethod
    def PrintTree():
        print('Tree View Ready')

    def FillTree(self):
        if self.JSonTable is None:
            pass
        elif isinstance(self.JSonTable, dict):
            for key, val in sorted(self.JSonTable.items()):
                self.new_item(self.TreeRoot, str(key), val)
        elif isinstance(self.JSonTable, (list, tuple)):
            for val in self.JSonTable:
                text = (str(val) if not isinstance(val, (dict, list, tuple))
                        else '[%s]' % type(val).__name__)
                self.new_item(self.TreeRoot, text, val)
        else:
            self.new_item(self.TreeRoot, str(self.JSonTable))

    def new_item(self, text, val=None):
        child = QTreeWidgetItem([text])
        child.setFlags(child.flags() | Qt.ItemIsEditable)

        self.FillTree(child, val)
        self.addChild(child)

        child.setExpanded(True)

   # This is meant to capture the On Change Event for the QTreeWidget
    def OnChange(self):
        print('Handling Changes Here for:',self.MyParent.JSonTable)
      # This routine would update your JsonTable with any changes
      # that take place within your TreeWidget however I do not 
      # think this is the correct function name to capture that
      # event so you might have to research this one a bit to get
      # the appropriate name

class MainWindow(QMainWindow):
    def __init__(self, JsonFilePath):
        super(MainWindow, self).__init__()

        self.setWindowTitle('Json File Editor')
        self.setGeometry(300, 100, 900, 600)

        self.JsonFile = JsonFilePath
        self.JSonTable = None

        self.CenterPane = ViewTree(self)
        self.setCentralWidget(self.CenterPane)

        self.CenterPane.PrintTree()
# Rem'd out because I could not test this for you 
# However it should work or... it might need tweaks
#        if len(self.JsonFile) > 0:
#            self.LoadFile()
        self.MainMenu = MenuToolBar(self)

    def OpenFile():
        self.JsonFile = QFileDialog.getOpenFileName()
      # Do not recall if QFileDialog returns None or not so you need to check that
        if len(self.JsonFile) > 0:
            self.LoadFile()

    def LoadFile():
      # Note one should always validate that they have a valid file prior to opening it
      # isfile() -- and checking the file extension are two methods I use
        JsonData = open(self.JsonFile[0],"r")
        self.JSonTable = json.load(JsonData)

        self.CenterPane.FillTree(self.JSonTable)

    def SaveFile():
      # Either to a new file or overwriting the exiting file
      # but basically you are now just saving your JsonTable
      # to file -- you could just loop through it manually or
      # I think there are wheels already invented to handle
      # Json objects like this and print them out to a file
        print('Saving Jason File')

def CmdLine():
  # create Parser object 
    Parser = argparse.ArgumentParser(description = "Load this Json File - Given the full file path")

  # defining arguments for Parser object 
    Parser.add_argument('-f', '--filepath', type = str, help = "This specifies the full path and filename for the Json File.") 

  # parse the argument if any from standard input
    CmdLineVal = Parser.parse_args().filepath
    RetVal = ''
    if CmdLineVal != None:
        RetVal = CmdLineVal

    return RetVal

if __name__ == '__main__':
    JsonFilePath = CmdLine()

    MainThred = QApplication([])

    MainGUI = MainWindow(JsonFilePath)
    MainGUI.show()

    sysExit(MainThred.exec_())

As a final note I did not test/validate your code as I assumed you understood what it does and will understand how to tweak it should it need tweaked to work with this framework