minecraft-assets/data/minecraft/worldgen/placed_feature/arboretum_trees.json

{
  "feature": "minecraft:arboretum_trees",
  "placement": [
    {
      "type": "minecraft:count_on_every_layer",
      "count": 12,
      "start_offset": 2
    },
    {
      "type": "minecraft:surface_water_depth_filter",
      "max_water_depth": 0
    },
    {
      "type": "minecraft:biome"
    }
  ]
}