How to use the slicer.mrmlScene.AddNode function in slicer

with open(tmp_segmentation_mha, 'wb') as f:
            f.write(__base64_decode__( data['content'] ))

        if sys.version_info.major == 2:
            # returnNode is deprecated in newer Slicer versions
            success, node = slicer.util.loadLabelVolume(tmp_segmentation_mha, properties={'show': False}, returnNode=True)
        else:
            node = slicer.util.loadLabelVolume(tmp_segmentation_mha, properties={'show': False})

        os.remove(tmp_segmentation_mha)

        logic = slicer.modules.volumerendering.logic()
        volumeNode = slicer.util.getNode(node.GetName())
        displayNode = logic.CreateVolumeRenderingDisplayNode()

        slicer.mrmlScene.AddNode(displayNode)
        displayNode.UnRegister(logic)
        logic.UpdateDisplayNodeFromVolumeNode(displayNode, volumeNode)
        volumeNode.AddAndObserveDisplayNodeID(displayNode.GetID())

        layoutManager = slicer.app.layoutManager()
        threeDWidget = layoutManager.threeDWidget(0)
        threeDView = threeDWidget.threeDView()
        threeDView.resetFocalPoint()

        for view in ['Red', 'Green', 'Yellow']:
            view_widget = slicer.app.layoutManager().sliceWidget(view)
            view_logic = view_widget.sliceLogic()

            view_logic.GetSliceCompositeNode().SetLabelVolumeID(node.GetID())

            view_logic.GetSliceCompositeNode().SetLabelOpacity(0.5)

def createAndObserveDisplayNode(node, displayNodeClass=slicer.vtkMRMLDisplayNode):
    displayNode = displayNodeClass()
    slicer.mrmlScene.AddNode(displayNode)
    node.SetAndObserveDisplayNodeID(displayNode.GetID())
    return displayNode

(LeftNode, RightNode) = self.logic.PatientModel.ClassifyLeftRight()
    
    # Update scene
    PriorLeft = slicer.util.getNode(LeftNode.GetName())
    if PriorLeft != None:
      self.LeftSideSelector.setCurrentNode(None)
      slicer.mrmlScene.RemoveNode(PriorLeft)
    
    PriorRight = slicer.util.getNode(RightNode.GetName())
    if PriorRight != None:
      self.RightSideSelector.setCurrentNode(None)
      slicer.mrmlScene.RemoveNode(PriorRight)    
    
    # Add new nodes to scene
    slicer.mrmlScene.AddNode(LeftNode)
    slicer.mrmlScene.AddNode(RightNode)
    
    LeftNode.CreateDefaultDisplayNodes()
    RightNode.CreateDefaultDisplayNodes()
    
    # Update user interface
    self.LeftSideSelector.setCurrentNode(LeftNode)
    self.RightSideSelector.setCurrentNode(RightNode)
    
    PriorSelectedSideNode = self.RepairSideSelector.currentNode()
    if PriorSelectedSideNode != None:
      self.RepairSideSelector.setCurrentNode(None)
      slicer.mrmlScene.RemoveNode(PriorSelectedSideNode)
      
      if PriorSelectedSideNode.GetName().__contains__("_Left"):
        self.RepairSideSelector.setCurrentNode(LeftNode)
      if PriorSelectedSideNode.GetName().__contains__("_Right"):

def setFOV2Largest2DRegion(self, widget, largestLabel=None, factor=1.5):
    if not largestLabel:
      largestLabel = self.findLargest2DRegion(self.segmentationNode)
    slicer.mrmlScene.AddNode(largestLabel)
    sliceLogic = widget.sliceLogic()
    sliceNode = sliceLogic.GetSliceNode()
    compositeNode = widget.mrmlSliceCompositeNode()
    savedVolumeID = compositeNode.GetBackgroundVolumeID()
    savedFOV = sliceNode.GetFieldOfView()
    compositeNode.SetBackgroundVolumeID(largestLabel.GetID())
    sliceLogic.FitSliceToAll()
    compositeNode.SetBackgroundVolumeID(savedVolumeID)
    FOV = sliceNode.GetFieldOfView()
    ModuleWidgetMixin.setFOV(sliceLogic, [FOV[0] * factor, FOV[1] * factor, FOV[2]])
    slicer.mrmlScene.RemoveNode(largestLabel)
    return largestLabel

def createMarkupAndDisplayNodeForFiducials(self):
    self.displayNode = slicer.vtkMRMLMarkupsDisplayNode()
    slicer.mrmlScene.AddNode(self.displayNode)
    self.inputMarkupNode = slicer.vtkMRMLMarkupsFiducialNode()
    self.inputMarkupNode.SetName('inputMarkupNode')
    slicer.mrmlScene.AddNode(self.inputMarkupNode)
    self.inputMarkupNode.SetAndObserveDisplayNodeID(self.displayNode.GetID())
    self.styleDisplayNode(self.displayNode)