How to make custom leaf blocks decay?

You can use tick update trigger to check for leaves in the surrounding and if there are none, remove the block.

decay? like falling leaves?

first of all: to create a leaf block you need to create texture with some transparents areas, and check the box "transparency" and select "CUTOUT_MIPPED" when create the block

EXAMPLE:
You Need to create a block texture with some transparent spaces like this image

but i don't understand "custom leaf blocks decay"