Import from BPMN2 in the Designer does not overwrite existing process

Issue

• I had imported a BPMN2 process by using Import from BPMN2 from designer.
  when we try to import second process then it can be imported without errors, but when we tried to build package, it failed with following exception

unable to parse xml : Exception class java.lang.IllegalArgumentException : A RuleFlowProcess cannot have more than one start node!