Display a tree node and begin its contents when open.
Parameters
label
string|Uint8Array
Widget label; interactive widgets also use it for ID
generation. A ## suffix can distinguish IDs without displaying the suffix.
Returns
boolean
True if the node is open and children should be submitted. Call
TreePop() after submitting those children.
Remarks
TreeNode functions return true when the node is open, in which case you
need to also call TreePop() when you are finished displaying the tree node
contents.
Display a tree node and begin its contents when open.