How do I make the faces I am using for the leaves of the tree I am making double sided? Currently only one side appears, while looking at them from a different angle they disappear. The only solution I have read so far is to duplicate the face and then flip the normal so you essentially have two faces back to back, but I'd rather not do this because I am trying to keep my poly count low, these trees are for a game.
For a game, I think that duplicating and flipping the normals is probably the best way to go.
Rendering double sided faces real-time is very expensive, probably more expensive than drawing the extra geometry.
It is possible however, enable Double sided in Properties > Object Data > Normals.