How can I view the root directory along with all its subdirectories in Finder?

Navigate to / (e.g. use ⌘+⇧+G.)
Then, in list view hold ⌥ while clicking the triangle. This will show all subdirectories of a certain folder.

By default, you'll don't see hidden files/directories. To show hidden files type the following commands in the Terminal.app:

defaults write com.apple.finder AppleShowAllFiles TRUE
killall Finder

You can use the value FALSE in the defaults write command to unto this action.

enter image description here

Finder - Preferences. Check the box to show your Mac there, and you will be able to easily navigate wherever you want.

Related