code: private void addCalendarDay(MpxjTreeNode parentNode, ProjectCalendar calendar, final Day day)
     {
        MpxjTreeNode dayNode = new MpxjTreeNode(day)
        {
           @Override public String toString()
           {
              return day.name();
           }
        };
        parentNode.add(dayNode);
        addHours(dayNode, calendar.getHours(day));
     }
docs: Add a calendar day node.
  
  @param parentNode parent node
  @param calendar ProjectCalendar instance
  @param day calendar day