I've used a 60 degree Onsrud Engraving bit (.01"flat) on all my VInlays, and even then if the board wasn't flat and finished...sometimes the very tiniest details where flat depth wasn't even close to being being approched....changed shape.
It would have been worse with a 90 degree as the angle is shallower.
A lot depends on the size and detail of the inlay though.
Some guys had started using 30 degree bits for that reason(haven't heard much back
I'll be trying a 30 engraving on my next on though,as I LOVE tiny detailed stuff.
IF I did this "Trees" again I'd definitely like a 30 0r 45 degree as I lost a couple leaves using the 60.