def init_tree(self, tree_alias, context):
        """Initializes sitetree in memory.

        Returns tuple with resolved tree alias and items on success.

        On fail returns (None, None).

        :param str|unicode tree_alias:
        :param Context context:
        :rtype: tuple
        """
        request = context.get('request', None)

        if request is None:
            raise SiteTreeError(
                'Sitetree requires "django.core.context_processors.request" template context processor to be active. '
                'If it is, check that your view pushes request data into the template.')

        if id(request) != id(self.current_request):
            self.init(context)

        # Resolve tree_alias from the context.
        tree_alias = self.resolve_var(tree_alias)
        tree_alias, sitetree_items = self.get_sitetree(tree_alias)

        if not sitetree_items:
            return None, None

        return tree_alias, sitetree_items
Initializes sitetree in memory.

        Returns tuple with resolved tree alias and items on success.

        On fail returns (None, None).

        :param str|unicode tree_alias:
        :param Context context:
        :rtype: tuple