Collapse/open tree structure

In any of the sheets there is a button on screen to open or collapse the entire tree structure, but is there a way to open/close just a specific level of the tree structure? For example I only want to collapse the lowest level of the structure so I don't have to see all of the sub-fixtures of my LED strips.

Also, are there any keyboard shortcuts for opening/closing the tree structure, or can it only be controlled by interacting with a mouse or touchscreen?

I'm not following. Using up/down left/right on the keyboard is just moving my selection box around in the fixture sheet.

I understand how to use up and down in regard to fixture selection and moving up and down through different levels of the tree for selection purposes. What I'm asking about is just closing one level of the tree visually.

Currently I'm using a bunch of LED strips that have 64 sub fixtures each. When browsing the fixture sheet, I find myself wanting to close just that level of the tree. But only way it seems to do that is to use the button at the top left of the sheet, which closes the entire tree and then I have to reopen the other top level groups to get back where I was.