def add_start_event_to_diagram(self, process_id, start_event_name="", start_event_definition=None,
                                   parallel_multiple=False, is_interrupting=True, node_id=None):
        """
        Adds a StartEvent element to BPMN diagram.

        User-defined attributes:

        - name
        - parallel_multiple
        - is_interrupting
        - event definition (creates a special type of start event). Supported event definitions -
            * 'message': 'messageEventDefinition', 
            * 'timer': 'timerEventDefinition', 
            * 'signal': 'signalEventDefinition',
            * 'conditional': 'conditionalEventDefinition', 
            * 'escalation': 'escalationEventDefinition'.

        :param process_id: string object. ID of parent process,
        :param start_event_name: string object. Name of start event,
        :param start_event_definition: list of event definitions. By default - empty,
        :param parallel_multiple: boolean value for attribute "parallelMultiple",
        :param is_interrupting: boolean value for attribute "isInterrupting,
        :param node_id: string object. ID of node. Default value - None.

        :return: a tuple, where first value is startEvent ID, second a reference to created object.
        """
        start_event_id, start_event = self.add_flow_node_to_diagram(process_id, consts.Consts.start_event,
                                                                    start_event_name, node_id)
        self.diagram_graph.node[start_event_id][consts.Consts.parallel_multiple] = \
            "true" if parallel_multiple else "false"
        self.diagram_graph.node[start_event_id][consts.Consts.is_interrupting] = "true" if is_interrupting else "false"
        start_event_definitions = {"message": "messageEventDefinition", "timer": "timerEventDefinition",
                                   "conditional": "conditionalEventDefinition", "signal": "signalEventDefinition",
                                   "escalation": "escalationEventDefinition"}
        event_def_list = []
        if start_event_definition == "message":
            event_def_list.append(BpmnDiagramGraph.add_event_definition_element("message", start_event_definitions))
        elif start_event_definition == "timer":
            event_def_list.append(BpmnDiagramGraph.add_event_definition_element("timer", start_event_definitions))
        elif start_event_definition == "conditional":
            event_def_list.append(BpmnDiagramGraph.add_event_definition_element("conditional", start_event_definitions))
        elif start_event_definition == "signal":
            event_def_list.append(BpmnDiagramGraph.add_event_definition_element("signal", start_event_definitions))
        elif start_event_definition == "escalation":
            event_def_list.append(BpmnDiagramGraph.add_event_definition_element("escalation", start_event_definitions))

        self.diagram_graph.node[start_event_id][consts.Consts.event_definitions] = event_def_list
        return start_event_id, start_event
Adds a StartEvent element to BPMN diagram.

        User-defined attributes:

        - name
        - parallel_multiple
        - is_interrupting
        - event definition (creates a special type of start event). Supported event definitions -
            * 'message': 'messageEventDefinition', 
            * 'timer': 'timerEventDefinition', 
            * 'signal': 'signalEventDefinition',
            * 'conditional': 'conditionalEventDefinition', 
            * 'escalation': 'escalationEventDefinition'.

        :param process_id: string object. ID of parent process,
        :param start_event_name: string object. Name of start event,
        :param start_event_definition: list of event definitions. By default - empty,
        :param parallel_multiple: boolean value for attribute "parallelMultiple",
        :param is_interrupting: boolean value for attribute "isInterrupting,
        :param node_id: string object. ID of node. Default value - None.

        :return: a tuple, where first value is startEvent ID, second a reference to created object.