Combining COUNTIF and LEFT Functions in Conditional Formatting

Hi. Essentially in my Excel sheet I want to create a border under cells in a column that share the same 2 first characters, but I do not know what those characters will be ahead of time and information will be added to the spreadsheet after the fact (so I CANNOT specify phrases).

I have used the COUNTIF function to do this bordering function under Conditional Formatting before and I expect the LEFT function is the solution to counting characters, but I cannot work out how to combine the formulas without knowing the specific information ahead of time.

This is my COUNTIF formula so far, would I add the character specification at the end, so instead of any one cell different it's identifying the initial different characters? =COUNTIF($D$2:$D2,$D2)=1

Any advice?