minecraft-assets/data/minecraft/recipe/bundle.json

{
  "type": "minecraft:crafting_shaped",
  "category": "equipment",
  "key": {
    "#": "minecraft:leather",
    "-": "minecraft:string"
  },
  "pattern": [
    "-",
    "#"
  ],
  "result": {
    "count": 1,
    "id": "minecraft:bundle"
  }
}