I would like to know the command for collapsing and expanding a branch in ttk.Treeview.

Here is a minimalistic example code:

#! coding=utf-8
import tkinter as tk
from tkinter import ttkroot = tk.Tk()
tree = ttk.Treeview(root)
tree.pack(fill=tk.BOTH,expand=True)tree.insert("", index="end",iid="Main", text="main branch")
tree.insert("Main", index="end", text="Stuff 1")
tree.insert("Main", index="end", text="Stuff 2")root.mainloop()

What command opens and/or expands the "main branch"? There has to be one, since these are called when clicking the plus and minus signs.

For me (Win 7, Py2.7), your example comes up with the branch closed, but you can open or close it as you like with this command:

tree.item("Main", open=False)

Set it to False to close it.

See these topics:

25.2. tkinter.ttk - Tk themed widgets - Item options

25.2. tkinter.ttk - Tk themed widgets - item method

Item options can be set either with insert(), or after the fact with item().