The feature is already available. Select any node in the Tree and press the - (minus) key on the numeric keypad to collapse all its sub-elements. Pressing the + (plus) key on the numeric keypad will expand it again to the previous view state.
Pressing the * (asterisk) on the keypad expands the entire sub-tree, regardless of the previous view-state, while pressing / (slash) collapses all sub-elements.
By the way, these are the same shortcuts as those used in Windows Explorer when navigating through folders and subfolders... just don't press * on your root C:\ folder, it takes an eternity to process! :p .
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Technical Product Manager
I don't want to achieve immortality through my work; I want to achieve immortality through not dying - Woody Allen