Firstborn/Assets/Editor/TreeReplacerS.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using UnityEditor;
// Replaces Unity terrain trees with prefab GameObject.
// http://answers.unity3d.com/questions/723266/converting-all-terrain-trees-to-gameobjects.html
[ExecuteInEditMode]
public class TreeReplacerS : EditorWindow {
    
    [Header("References")]
    public Terrain _terrain;

    [MenuItem("Schaken-Mods/Tree Replacer Tool")]

    static void Init() {
        TreeReplacerS window = (TreeReplacerS)GetWindow(typeof(TreeReplacerS));
    }

    void OnGUI() {
        _terrain = (Terrain)EditorGUILayout.ObjectField(_terrain, typeof(Terrain), true);
        if (GUILayout.Button("Convert to objects")) {
            Convert();
        }
        if (GUILayout.Button("Clear generated trees")) {
            Clear();
        }
    }

    public void Convert() {
        TerrainData data = _terrain.terrainData;
        float width = data.size.x;
        float height = data.size.z;
        float y = data.size.y;
        // Create parent
        GameObject parent = GameObject.Find("Object_Cluster");
        if (parent == null)
        {
            parent = new GameObject("Object_Cluster");
        }
        // Create trees
        foreach (TreeInstance tree in data.treeInstances)
        {
            if (tree.prototypeIndex>=data.treePrototypes.Length)
                continue;
            var _tree = data.treePrototypes[tree.prototypeIndex].prefab;
            Vector3 position = new Vector3(
                tree.position.x * width,
                tree.position.y*y,
                tree.position.z * height) + _terrain.transform.position;
            Vector3 scale = new Vector3(tree.widthScale,tree.heightScale,tree.widthScale);
            GameObject go = Instantiate(_tree, position, Quaternion.Euler(0f,Mathf.Rad2Deg*tree.rotation,0f), parent.transform) as GameObject;
            go.transform.localScale  = scale;
        }
    }

    public void Clear() {
        DestroyImmediate(GameObject.Find("Object_Cluster"));
    }
}