Intentionally Duplicating Data

[AdamBroom]

I have a list of data in column B

I'd like every cell in column B repeated twice in column A

E.g.
A1=B1
A2=B1
A3=B2
A4=B2

Have tried typing this in this simply and using auto fill but auto fill always interprets as the cell to the right i.e. A3=B3 meaning B2 data is lost

Is there a formula that I can use instead?

[#2]

Try this formula in A1, copied down rows:
=INDEX(B:B,
CEILING(ROW(B1)/2,1))