Terrain.treeCrossFadeLength

Description

Total distance delta that trees will use to transition from billboard orientation to mesh orientation.

Decreasing this value makes the transition happen faster. Setting it to 0 will produce a visible pop when switching from mesh to billboard representation.

using UnityEngine;

public class Example : MonoBehaviour
{
    void Start()
    {
        Terrain.activeTerrain.treeCrossFadeLength = 20;
    }
}