'Get a tree.
:param str sha: (required), sha of the object for this tree
:returns: :class:`Tree <github3.git.Tree>`'

def tree(self, sha):

    json = None
    if sha:
        url = self._build_url(u'git', u'trees', sha, base_url=self._api)
        json = self._json(self._get(url), 200)
    return self._instance_or_null(Tree, json)
