如何在kivy/KivyMD的文本输入中插入文本？

from kivy.uix.textinput import TextInput
from kivymd.app import MDApp
from kivy.lang import Builder

KV = '''
BoxLayout:
    orientation: 'vertical'

    TextInput:
        id: my_textinput
        multiline: True

    Button:
        text: '插入文本'
        on_release: app.insert_text()
'''

class MyApp(MDApp):
    def build(self):
        return Builder.load_string(KV)

    def insert_text(self):
        textinput = self.root.ids.my_textinput
        current_text = textinput.text
        new_text = "要插入的文本"
        textinput.text = current_text + new_text

if __name__ == '__main__':
    MyApp().run()