Validation Source Variable Based On Criteria

I need two columns of "expense types": the first uses an Excel Validation drop down based on a list of 4 items; the second column needs to be another Validation drop down based on lists that are variable depending on the selection of the 1st column... ie: 1st column: user selects "overhead", 2nd column no adjusts list to only allow "pencils","paper","staples", however if the first column choice was "travel", now the second column options would be "auto","air","train".

thank you very much!!!!!!!!!!!!!!!!!!!!!!!!!