Class method that opens (load) a vntree pickle file.

        :param filepath: the file path for the pickle file. 
        :type filepath: str         
        :returns: root node of tree or `False` if failure. 
        :rtype: Node or bool

def openfile(cls, filepath):
        """Class method that opens (load) a vntree pickle file.

        :param filepath: the file path for the pickle file. 
        :type filepath: str         
        :returns: root node of tree or `False` if failure. 
        :rtype: Node or bool
        """
        if not os.path.isfile(filepath):
            logger.error("%s.openfile: arg `filepath`=«%s» not valid." % (cls.__name__, filepath))
            return False
        try:
            with open(filepath, "rb") as pf:
                pkldata = pickle.load(pf)
            rootnode = cls(treedict=pkldata)
            rootnode._vnpkl_fpath = os.path.abspath(filepath)
        except Exception as err:
            logger.error("%s.openfile: data in file «%s» not valid: %s" % (cls.__name__, filepath, err))
            return False
        return rootnode