Two-Step form in HubSpot

hubspot-2step-form.html

<h1>2 Step Form</h1>
<div id="demo-form"></div>
<script charset="utf-8" type="text/javascript" src="https://js.hsforms.net/forms/v2.js"></script>
<script>
  var data = []

  hbspt.forms.create({
  portalId: "YOUR_PORTAL_ID_HERE",
  formId: "STEP_ONE_FORM_ID_HERE",
  target: "#demo-form",
  onFormSubmit: function(form) {
    var incoming = $(form).serializeArray();
    data.push(incoming);
  },
  onFormSubmitted: function(form) {
    $('#demo-form').empty();
    hbspt.forms.create({
      portalId: "YOUR_PORTAL_ID_HERE",
      formId: "STEP_TWO_FORM_ID_HERE",
      target: "#demo-form",
      onFormReady: function(form) {
        form.find('input[name="email"]').val(data[0].value).change();
      }    
    })
  }
});
</script>

Hi, how can we add a progress bar in this multi step form?