minecraft-assets/data/minecraft/worldgen/configured_feature/trees_plains.json

{
  "type": "minecraft:random_selector",
  "config": {
    "default": {
      "feature": "minecraft:oak_bees_005",
      "placement": []
    },
    "features": [
      {
        "chance": 0.33333334,
        "feature": {
          "feature": "minecraft:fancy_oak_bees_005",
          "placement": []
        }
      }
    ]
  }
}