make leaves get a random level when they start decomposing.

mods/bg_tree/decompose.lua

@@ -23,7 +23,10 @@ blockgame.register_increasing_abm({
 		return data.value >= 80
 	end,
 	action = function (pos, node, data)
-		minetest.set_node(pos, {name = leaves_decomposing})
+		-- NOTE: might wanna access the 4 from somewhere, instead of directly knowing it.
+		-- that way this won't have to change if decomposing leaves max levels change.
+		local level = math.random(1, 4)
+		minetest.set_node(pos, {name = leaves_decomposing .. "_" .. level})
 	end,
 })