概要

using UnityEditor;
using UnityEditor.SceneTemplate;
using UnityEngine;

public static class Example
{
    [MenuItem( "Tools/Hoge" )]
    private static void Hoge()
    {
        var sceneTemplateAssetPath = "【.scenetemplate のパス】";
        var scenePath              = "【.unity のパス】";
        var sceneTemplateAsset     = AssetDatabase.LoadAssetAtPath<SceneTemplateAsset>( sceneTemplateAssetPath );
        var result                 = SceneTemplateService.Instantiate( sceneTemplateAsset, false, scenePath );

        Debug.Log( result.scene );
        Debug.Log( result.sceneAsset );
    }
}