I personally prefer not to create new shortcuts. As @Mark pointed out on the answer of @JayChase there is an existing shortcut, but it requires the explorer to be in focus. Therefore I combine the shortcut mentioned by @JayChase with another standard shortcut, to get the desired behaviour.
command + 0(focusses on explorer).command + left-arrow
An additional benefit over this approach is that I usually want to focus on the explorer view if I want to collapse the folders.