Paste_Image.png
reference：
1，http://stackoverflow.com/questions/8304172/tree-command-on-osx-bash
2，http://web.archive.org/web/20130527203022/http://shaunchapman.me/post/329270449/how-to-install-the-tree-command-on-mac-os-x
3，http://mama.indstate.edu/users/ice/tree/
