add trigger to data group

        Parameters
        ----------
        group : int
            group index
        timestamp : float
            trigger time
        pre_time : float
            trigger pre time; default 0
        post_time : float
            trigger post time; default 0
        comment : str
            trigger comment

def add_trigger(self, group, timestamp, pre_time=0, post_time=0, comment=""):
        """ add trigger to data group

        Parameters
        ----------
        group : int
            group index
        timestamp : float
            trigger time
        pre_time : float
            trigger pre time; default 0
        post_time : float
            trigger post time; default 0
        comment : str
            trigger comment

        """
        comment_template = """<EVcomment>
    <TX>{}</TX>
</EVcomment>"""
        try:
            group = self.groups[group]
        except IndexError:
            return

        trigger = group.trigger

        if comment:
            try:
                comment = ET.fromstring(comment)
                if comment.find(".//TX"):
                    comment = comment.find(".//TX").text
                else:
                    comment = ""
            except ET.ParseError:
                pass

        if trigger:
            count = trigger["trigger_events_nr"]
            trigger["trigger_events_nr"] += 1
            trigger.block_len += 24
            trigger[f"trigger_{count}_time"] = timestamp
            trigger[f"trigger_{count}_pretime"] = pre_time
            trigger[f"trigger_{count}_posttime"] = post_time
            if comment:
                if trigger.comment is None:
                    comment = f"{count + 1}. {comment}"
                    comment = comment_template.format(comment)
                    trigger.comment = comment
                else:
                    current_comment = trigger.comment
                    try:
                        current_comment = ET.fromstring(current_comment)
                        if current_comment.find(".//TX"):
                            current_comment = current_comment.find(".//TX").text
                        else:
                            current_comment = ""
                    except ET.ParseError:
                        pass

                    comment = f"{current_comment}\n{count + 1}. {comment}"
                    comment = comment_template.format(comment)
                    trigger.comment = comment
        else:
            trigger = TriggerBlock(
                trigger_event_nr=1,
                trigger_0_time=timestamp,
                trigger_0_pretime=pre_time,
                trigger_0_posttime=post_time,
            )
            if comment:
                comment = f"1. {comment}"
                comment = comment_template.format(comment)
                trigger.comment = comment

            group.trigger = trigger