Fix bt node sizing on spawm

Source/Editor/Surface/Archetypes/BehaviorTree.cs

@@ -121,6 +121,14 @@ namespace FlaxEditor.Surface.Archetypes
                 UpdateTitle();
             }
 
+            /// <inheritdoc />
+            public override void OnSpawned()
+            {
+                base.OnSpawned();
+
+                ResizeAuto();
+            }
+
             /// <inheritdoc />
             public override void ResizeAuto()
             {