How to make leaves transparent

Hello,

When I create a custom tree leaves are just falling off the tree in the custom biomes and causing lag and trees without leaves if i Select the option leaves in the first page of the custom block.When I select default basic block,the transparent parts on the texture are black.If I select translucent;cuttout or cuttout mipped,we can see through the blocks behind,who made an X-ray item.I don't know haw to fix it!