Usually you can limit a oak tree to not grow the "fancy oak tree" variation which has branches by placing a block 8 blocks above the sapling

however if the sapling is at -2 or lower it is still capable of growing this variation unless you place the block 7 blocks above the sapling. this inconsitency doesnt make sense and breaks a lot of tree farms if they are build in negative y heights

 i tested this in vanilla minecraft without any mods and included a test setup to reproduce it in the attached world download