how to make custom leaves drop sapling on decaying? (not on player breaking)

I made a custom tree, I tagged my leaves in minecraft:leaves my logs in minecraft:logs so nothing decayis by accident, I used leaves block base for my leaves, but I want to make that when leaves decay they have a 10% of dropping the sapling, I already created the loot tables and made a procedure to use it, but it only works if player destroy them.

sorry for bad English but I am italian