$ brew install tree
Result:
Error: /usr/local is not writable. You should change the ownership
and permissions of /usr/local back to your user account:
sudo chown -R $(whoami) /usr/local
Warning: You are using OS X 10.12.
We do not provide support for this pre-release version.
You may encounter build failures or other breakages.
Please create pull-requests instead of filing issues.
Error: Your Xcode (7.3.1) is outdated
Please update to Xcode 8.0.
Xcode can be updated from
https://developer.apple.com/xcode/downloads/
If 8.0 is installed, you may need to:
sudo xcode-select --switch /path/to/Xcode-beta.app