minecraft-assets/data/minecraft/worldgen/template_pool/village/plains/trees.json

{
  "elements": [
    {
      "element": {
        "element_type": "minecraft:feature_pool_element",
        "feature": "minecraft:oak",
        "projection": "rigid"
      },
      "weight": 1
    }
  ],
  "fallback": "minecraft:empty",
  "name": "minecraft:village/plains/trees"
}