title: Chart with multi-level labels on x-axis
body: <p>I'm creating a VSTO add-in that among other things is supposed to create a line chart for some annual data. This data contains datapoints on a weekly basis. I would like the horizontal axis to be grouped in months, illustrated here:</p>
  
  <p><a href="https://i.stack.imgur.com/w7Ozi.png" rel="noreferrer"><img src="https://i.stack.imgur.com/w7Ozi.png" alt="enter image description here"></a></p>
  
  <p>I can't however find anything in the VSTO documentations about whether this is possible or not. As far as I can tell a <a href="https://msdn.microsoft.com/en-us/library/microsoft.office.interop.powerpoint.series_members(v=office.14).aspx" rel="noreferrer">Series</a> only takes a 1-dimensional array of values for the X-axis. Does anyone have any experience with this?</p>