[Tkinter] About Tkinter Treeview.selection_get() usage.

[water]

Tkinter Treeview widget has selection_get, but document not introduce about that, how to use it?

from tkinter import Tk, ttk
root_ = Tk()
tree1 = ttk.Treeview(root_, height = 10, selectmode = 'browse')
tree1.insert('', 'end', text = 'item 0')
tree1.insert('', 'end', text = 'item 1')
tree1.insert('', 'end', text = 'item 2')
tree1.insert('', 'end', text = 'item 3')

tree1.selection_get()

Error:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Program Files\Python310\lib\tkinter\__init__.py", line 1007, in selection_get
    return self.tk.call(('selection', 'get') + self._options(kw))
_tkinter.TclError: PRIMARY selection doesn't exist or form "STRING" not defined