Editor Scene Setup Almost Functional

Editor/EditorSceneSetup/EditorSceneSetup.cs

-using System.Collections;
-using System.Collections.Generic;
+using UnityEngine.SceneManagement;
+using UnityEditor.Callbacks;
+        [OnOpenAsset]
+        static bool OnOpenAsset(int instanceID, int line)
+        {
+            var obj = EditorUtility.InstanceIDToObject(instanceID);
+            if(obj is EditorSceneSetup)
+            {
+                EditorSceneSetup setup = (EditorSceneSetup)obj;
+                int active = setup.ActiveScene;
+
+                try
+                {
+                    for (int i = 0; i < setup.LoadedScenes.Length; i++)
+                    {
+                        var scene = setup.LoadedScenes[i];
+                        EditorUtility.DisplayProgressBar("Loading Scenes", string.Format("Loading {0}", scene.Scene.name), (float)i / setup.LoadedScenes.Length - 1);
+                        var path = AssetDatabase.GetAssetPath(scene.Scene);
+                        EditorSceneManager.OpenScene(path, i == 0 ? OpenSceneMode.Single : (scene.Loaded ? OpenSceneMode.Additive : OpenSceneMode.AdditiveWithoutLoading));
+                    }
+                    EditorUtility.DisplayProgressBar("Loading Scenes", "Set Active Scene", 1.0f);
+                    SceneManager.SetActiveScene(EditorSceneManager.GetSceneAt(active));
+                }
+                finally
+                {
+                    EditorUtility.ClearProgressBar();
+                }
+            }
+            return true;
+        }
+
+
         [MenuItem("Assets/Create/Editor Scene Setup", priority = 200)]
         public static void CreateAsset()
         {

Editor/EditorSceneSetup/EditorSceneSetupEditor.cs

                 m_LoadedScenes.GetArrayElementAtIndex(index).FindPropertyRelative("Scene").objectReferenceValue = sceneAsset;
             }
 
+            EditorGUI.BeginDisabledGroup(index == 0);
             int visible = m_LoadedScenes.GetArrayElementAtIndex(index).FindPropertyRelative("Loaded").boolValue ? 1 : 0;
             visible = EditorGUI.IntPopup(loadedRect, visible, kLoadedItems, kLoadedIndices);
 
+            } else if(index == 0)
+            {
+                m_LoadedScenes.GetArrayElementAtIndex(index).FindPropertyRelative("Loaded").boolValue = true;
-
+            EditorGUI.EndDisabledGroup();
             serializedObject.ApplyModifiedProperties();
         }