Shears Functionality

I am making new leaves for my tree and using loot table drops, i already made it drop sapling at a chance and drop its self when using silk touch. but i can't figure out how to make it so the leaf block drops when using shears

EDIT: i know how to detect if the player is holding shears when the block is broken but i don't know how to make it so the items from the loot table don't duplicate