Yup, simply make the background to the leaves completely green instead of white. (simply put a green layer behind it - the alpha channel will still be saved if its there under "channels".)
Its pretty much the same reason as for why one needs to have a bleeding edge around uv shells on the texture: When the mipmaps (= automatic low-res versions of the texture used when the object is far away) are generated, the color of a new pixel is calculated through the average color of the pixels that used to be in its place on the higher res version. Thus, a pixel thats at the border between green and white becomes a greyish-green and you get ugly edges. (On a transparent png it probably assumes a default color for the transparent pixels, which is white.)
Quote: Also, Blender shows both sides of the texture (For the leaves) in the viewport. But I guess Amnesia doesn't support this, so my tree will look a bit screwed up.
Is their any way I can mimic this in Blender? I can't really tell which side will be shown in Amnesia.
Never worked in Blender, but to see which side of a polygon is the "right one" (= the only one that engines will show) search for something called "backface culling" or the like. As for making both sides visible in hpl, you need two polygons for that - this is what I'd do in general:
1. select all leaf polygons
2. duplicate them
3. flip the face normals of the duplicates
It will probably look like a flickering mess in blender, if backface culling is turned off and it's still drawing both sides of the polygons, but when hpl only draws the "right" side later, it should look fine.