code: function append_nested(concater,items){
      concater += `\\begin{enumerate}\n`;
      for(var index in items){
          concater += `\\item ${items[index].name}\n`;
          // doing append job
          if(items[index].subitems != undefined){
              concater = append_nested(concater,items[index].subitems); 
          }
      }
      concater += `\\end{enumerate}\n`;
      return concater;
  }
docs: list structure operation