在用户定义的类中调用init项目时，我会收到一个属性

Question

class Schedule():
    def __init__(self,  master):
        self.master = master
        master.title('Schedule')
        master.geometry('800x800')
        self.Main = Frame(self.master)
        self.Main.pack(fill = BOTH)

        #Widgets        
        self.treeFrame = Frame(self.Main, height = 690, width = 800)
        self.treeFrame.pack(side = BOTTOM, expand = False)
        self.PGvariable = StringVar()
        self.PGvariable.set(ProduktionsGruppe[0])
        self.ProduktionsGruppeOptionMenu = OptionMenu(self.optionsFrame, self.PGvariable, 
                    'Gruppe auswählen', *ProduktionsGruppe.values(), command = Schedule.selectPG)
        self.ProduktionsGruppeOptionMenu.pack(pady = 10)


        self.tree = Treeview(self.treeFrame, show = 'headings', height = 32)

        self.selectPG()


    def selectPG(self):
        
        #delete existing tree
        for i in self.tree.get_children():
            self.tree.delete(i)
        
        #get production group selection
        PGselection = self.PGvariable.get()
        global PGselectionint
        self.PGvariable.set(ProduktionsGruppe[PGselectionint])
        
        #create tree with list of selected group's names as columns
        treeview_columns = listofnumberlists[PGselectionint]
        self.tree['columns'] = treeview_columns

if __name__ == '__main__':
    root = Tk()
    Schedule(root)
    root.mainloop()

这是代码的相关部分。它旨在显示一个可以通过用户从OptionMenu选择选项来更改的树视图。当我运行它时，它会恰好提起TreeView，但是当我从选项菜单中选择一个选项时，我会在此属性中出现

for i in self.tree.get_children():
AttributeError: 'str' object has no attribute 'tree'

相同的错误，在我尝试从 init 在类中的不同功能中函数。 有人知道如何解决这个问题吗？