use bevy_spatial::{AutomaticUpdate, KDTree3, TransformMode, SpatialAccess};

#[derive(Component, Default)]
struct TrackedByKDTree;

fn main() {
    App::new()
        .add_plugins(AutomaticUpdate::<TrackedByKDTree>::new()
            .with_frequency(Duration::from_secs_f32(0.3))
            .with_transform(TransformMode::GlobalTransform))
        .add_systems(Update, use_neighbour);
    // ...
}

type NNTree = KDTree3<TrackedByKDTree>; // type alias for later

// spawn some entities with the TrackedByKDTree component

fn use_neighbour(tree: Res<NNTree>){
    if let Some((pos, entity)) = tree.nearest_neighbour(Vec3::ZERO) {
        // pos: Vec3
        // do something with the nearest entity here
    }
}