highcharts - highcharts add more data in tooltip

Question

I'm working on a bar chart. I want to add additional data series in tooltip. I found I can create another series and set visible as false. But that is not what I want because it will show on the chart. I have a series like below:

  'series' : [
    {
        'name': '1 month ago ',
        'data': last_val

    },
    {
        'name': 'Current ',
        'data': current_val

    }            
  ]

last_val and current_val are two arrays. I want to add two additional data array in tooltip, my question is can I put the additional array as part of data in this series? How can I do that?