To use the dialog content, the first level of the "tree" must always be expanded, thus should be expanded upon entry to the dialog instead of having the user perform this step repeatedly.
... and then, after countless encounters of the "tree" being collapsed, it's now expanded when entering the dialog.
... but now it's not! {Puzzled}.
Far later, it seems the standard behavior ends up (mostly) being that the tree is collapsed.
Another little quirk in the dialog that I stumble into often is that I use Enter to expand a node, but unless it is a Handle or ID node that is active, the focus is just shifted to the code editor and creates a little extra hassle.
Enter on a parent node should preferably only open the node.