Custom Inspector when Selecting from Project Tree?

I have created a custom editor that can create a special asset. It is meant to be a blueprint / predefined asset that you can assign to the characters in my game. (Not a component because you edit them visually.) It is created from the Menu as follows:

 // Create a new Behavior Tree
 [MenuItem("GameObject/Create Other/Behavior Tree")]
 static void CreateTree()
 {
     Init();

     BehaviorTree newTree = new BehaviorTree();
     m_behaviorTrees.Add(newTree);
     m_selectedTree = newTree;
     Selection.activeObject = newTree;

     AssetDatabase.CreateAsset(newTree, "Assets/TestTree.tree.asset");// <-- .asset
 }

When you select a script in the editor or a texture it brings up a special Inspector for those types. How can I make my custom asset respond with a custom inspector when you select it from the Project Tree (the tree with Scripts.)

Here is my custom Inspector:

 [CustomEditor(typeof(BehaviorTree))]
 public class BehaviorTreeInspector : Editor
 {
     SerializedProperty m_nodes;
     
     public void OnEnable()
     {
         m_nodes = serializedObject.FindProperty("Nodes");
     }
 
     // Implement this function to make a custom inspector.
     public override void OnInspectorGUI()
     {
         if (GUILayout.Button("Add Node"))
         {
         Debug.Log("New node added!");
         BehaviorTree tree = target as BehaviorTree;
         tree.AddNode();
         }
         GUILayout.TextArea("Yes!");
     }
 }