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

{
  "type": "minecraft:random_selector",
  "config": {
    "default": "minecraft:spruce_on_snow",
    "features": [
      {
        "chance": 0.33333334,
        "feature": "minecraft:pine_on_snow"
      }
    ]
  }
}