python tkinter 无法自动关闭

Question

tkinter root.withdraw()之后中间做了其他事情，下面重新要用tkinter 显示processbar， 用了root.wm_deiconify
点击start 完成4 个file 合并之后， 不能自动退出。
后面的程序也被打断不能执行到底。

    root = tkinter.Tk()
    root.title('Step 1 of 4') 
    root.geometry('300x280+600+300')
    root.withdraw()     


************************中间做了其他事情下面重新要用tkinter 显示processbar。

    root.wm_deiconify()
    pb = ttk.Progressbar(root, length =200, maximum = 100)
    pb.pack(padx=10,pady=20)#pb.grid(row = 0, column = 1)   
    
    def start():
        global mergeSingleV,mergeStableV,mergeSingleM,mergeSingleMStep,mergeStableM,mergeOther        
        mergeSingleV = mergeStableV = mergeSingleM = mergeSingleMStep = mergeStableM = mergeOther = EE.create_df_type()
        # mergeSingleV = EE.create_df_type()
        # mergeStableV = EE.create_df_type()
        # mergeSingleM = EE.create_df_type()
        # mergeSingleMStep = EE.create_df_type()
        # mergeStableM = EE.create_df_type()
        # mergeOther = EE.create_df_type()
        mergeSingleV = mergeStableV = mergeSingleM = mergeSingleMStep = mergeStableM = mergeOther = EE.create_df_type()
        for i in range(0,len(files)):
            print(files[i])  
            tracepath = os.path.join(tracedir,files[i])                           
            data = pd.read_csv(tracepath,index_col= False) 
            data['Filename'] = files[i]
            data = data.merge(configP[['Par','AnalyClass']],on ='Par', how='left') 
            data = data.merge(configS[['Par','Step','AnalyClass']], on=['Par','Step'],how='left') # AnalyClass_x, AnalyClass_y 
            data['Class'] = np.where(data['AnalyClass_x'].notnull(), data['AnalyClass_x'], data['AnalyClass_y'])# Bug here AnalyClass_y failed                    
            singleV = data[data['Class']==1].drop(['AnalyClass_x','AnalyClass_y'],axis=1) # only ok4 file# na 'Parameter'
            stableV = data[data['Class']==2].drop(['AnalyClass_x','AnalyClass_y'],axis=1) # dplyr::filter(data, class==2)[,1:5]
            singleM = data[data['Class']==3].drop(['AnalyClass_x','AnalyClass_y'],axis=1) #,'Parameter'
            singleMStep = data[data['Class']==4].drop(['AnalyClass_x','AnalyClass_y'],axis=1) #?? 空
            stableM = data[data['Class']==5].drop(['AnalyClass_x','AnalyClass_y'],axis=1) 
            other = data[data['Class'].isnull()].drop(['AnalyClass_x','AnalyClass_y'],axis=1) 
            
            mergeSingleV = mergeSingleV.append(singleV) # <- rbind(mergeSingleV,singleV)# cbind() 把矩阵横向合并成一个大矩阵（列方式），而rbind()是纵向合并（行方式）。
            mergeSingleV[['Step','Interval']] = mergeSingleV[['Step','Interval']].astype(float)
            mergeStableV = mergeStableV.append(stableV) #keep data width and data columns the same for appending
            mergeSingleM = mergeSingleM.append(singleM) #Filename 
            mergeSingleMStep = mergeSingleMStep.append(singleMStep)# Last column:Filename not Class
            mergeStableM = mergeStableM.append(stableM) 
            mergeOther = mergeOther.append(other)            

            pb['value'] += 100/len(files)
            print(pb['value'])
            pb.update() # 更新画面
            
    bnt = ttk.Button(root, text = 'start',command= start)#bnt2 = ttk.Button(root, text="Quit", command=quit)
    bnt.pack(pady=10) #bnt.grid(row = 0, column = 0)#bnt2.grid(row = 1, column = 1)
    draw_button = ttk.Button(root, text="Quit", command = EE.close_window)
    draw_button.pack(pady=20)
    root.mainloop() #启动应用程序，启动消息循环