add alias 'tree'

    * http://qiita.com/yone098@github/items/bba8a42de6b06e40983b?utm_source=Qiita%E3%83%8B%E3%83%A5%E3%83%BC%E3%82%B9&utm_campaign=5770942720-Qiita_newsletter_127_22_10_2014&utm_medium=email&utm_term=0_e44feaa081-5770942720-32743205