Version: 2018.1
public static bool IsMainAsset (Object obj);
public static bool IsMainAsset (int instanceID);

説明

アセットがプロジェクトウインドウでメインのアセットかどうか。

For example an imported model has a game object as its root and several Meshes and child game objects in expanded state. The root game object is the main asset in this case.