Add "ALL" in dropdown, and show exists choices form, but not change data side

[JennyT]

I have a business unit choice, in Choices('Business Unit'), which already has [Program, Information, Support, Public Health] 4 columns. I have a drop-down and set 'item' as Choices('Business Unit'), it shows [Program, Information, Support, Public Health]. 

I want to add "ALL" as a column in the dropdown with [Program, Information, Support, Public health] but not change the database side only in this screen( because I also use business unit choice in other places), so the final dropdown want be ["ALL", "Program", "Information", "Support", "Public Health" ]. It might be adding more choice column in the future, so want to use Choices('Business Unit'), then it will be automatically added. 

Thank you so much!!! 

[TheRobRush · Accepted solution]

@RandyHayes actually made a wonderful video on this adding all to a dropdown list, give it a watch!

Add an "All" to Your Dropdown Lists - Dynamically! 

[JennyT]

That's exactly what I need! Thank you!!!