some_treasure.json

{
    "rolls": {
        "min": 2,
        "max": 6
    },
    "items": {
        "minecraft:diamond" : {
            "weight": 5,
            "count" : [2, 7]
        },
        "minecraft:saddle" : {
            "weight": 3
        },
        "minecraft:iron_pickaxe" : {
            "weight": 3,
            "enchant_with_levels" : {
                "treasure": true,
                "levels" : [20, 39]
            }
        }
        And so on...
    }
}