Terrain.treeDistance

Description

The maximum distance at which trees are rendered.

The higher this is, the further the distance trees can be seen and the slower it will run.

Additional resources: Terrain.treeBillboardDistance.

using UnityEngine;

public class Example : MonoBehaviour
{
    void Start()
    {
        Terrain.activeTerrain.treeDistance = 2000;
    }
}