ArgumentException: GameObject is already part of target prefab
UnityEditor.PrefabUtility.AddGameObjectsToPrefabAndConnect (UnityEngine.GameObject[] gameObjects, UnityEngine.Object targetPrefab) (at /Users/bokken/build/output/unity/unity/Editor/Mono/Prefabs/PrefabUtility.bindings.cs:316)
UnityEditor.PrefabUtility.ApplyAddedGameObjects (UnityEngine.GameObject[] gameObjects, System.String assetPath, UnityEditor.InteractionMode action) (at /Users/bokken/build/output/unity/unity/Editor/Mono/Prefabs/PrefabUtility.cs:1983)
UnityEditor.PrefabUtility.ApplyAddedGameObject (UnityEngine.GameObject gameObject, System.String assetPath, UnityEditor.InteractionMode action) (at /Users/bokken/build/output/unity/unity/Editor/Mono/Prefabs/PrefabUtility.cs:1930)
UnityEditor.SceneManagement.AddedGameObject.Apply (System.String prefabAssetPath, UnityEditor.InteractionMode mode) (at /Users/bokken/build/output/unity/unity/Editor/Mono/Prefabs/PrefabOverrides/PrefabOverride.cs:189)
UnityEditor.SceneManagement.PrefabOverride.Apply (System.String prefabAssetPath) (at /Users/bokken/build/output/unity/unity/Editor/Mono/Prefabs/PrefabOverrides/PrefabOverride.cs:22)
UnityEditor.PrefabOverridesTreeView+ComparisonViewPopup.Apply (System.Object prefabAssetPathObject) (at /Users/bokken/build/output/unity/unity/Editor/Mono/Prefabs/PrefabOverrides/PrefabOverridesTreeView.cs:822)
UnityEditor.GenericMenu.CatchMenu (System.Object userData, System.String[] options, System.Int32 selected) (at /Users/bokken/build/output/unity/unity/Editor/Mono/GUI/GenericMenu.cs:160)