Stylized foliage Material Pack for your tree and bush 

You con customize the size, color, pattern, shadow and more.

You can use custom mesh but your mesh need to have 1 uvshell for each polygon and each UV shell need to be a 1;1 square who take all the uv space.

You can do this in Maya with the "Unitize" function in UV\UV editor\Modify\Unitize, you can also do this in Zbrush with the Uv Map\Create\UV Tile