Menu Tree - How to Cover Parent Items

When using nested item lists in the menu tree, the parent items are not covered and it makes it harder to determine the currently selected item options.

How can I fill the space below the current menu options, hiding the parent list?

Parent List:

Parent selected with child list showing (and what I don't want):

I would prefer to have the pane filled to the bottom of the screen just like the parent items list does. How can this be accomplished?

Ignition 8.1.43, Perspective dock.