How to use multiple excel files as data source for unit test in C#?

I am trying to make a unit test that have data source from multiple excel files, each excel file contains a test case for the same unit test. I would like to put all the excel files in one folder and let the unit test program to iterate through all the excel files.

I have found several methods, like storing all the test cases in a XML file but this method is too tedious as I have to extract all the test cases from the excel files and put it into the same XML file. I hope to get an efficient way to do it. Any suggestions?