I don't think that is possible else you would simultaneously be entertaining two values for a given month.
However, you may be able to do something similar with a variation of a Column format; especially if you format it to show no overlap
Can you give me an example of how I can do that? I am not sure what
you mean column format?
Insert / Charts / Column / 2D columns
Then, within the chart, select the Data series and / Format Data Series
Series Options: Gap Width set to "No Gap" or 0%
Fill: Set to Solid Fill and pick an attractive color
Border Color: Leave at automatic or experiment.