diff --git a/README.md b/README.md
index da263c6..d3b52f7 100644
--- a/README.md
+++ b/README.md
@@ -29,6 +29,8 @@ php artisan filament:assets
 ## Usage
 
 ```PHP
+use CodeWithDennis\FilamentSelectTree\SelectTree;
+
 // Create a tree based on a 'BelongsToMany' relationship
 SelectTree::make('categories')
     ->relationship('categories', 'name', 'parent_id', function ($query) {
diff --git a/src/SelectTree.php b/src/SelectTree.php
index bf1623e..31907b3 100644
--- a/src/SelectTree.php
+++ b/src/SelectTree.php
@@ -45,7 +45,7 @@ class SelectTree extends Field
 
     protected ?Closure $modifyQueryUsing;
 
-    protected Closure|int $defaultOpenLevel;
+    protected Closure|int $defaultOpenLevel = 0;
 
     protected string $direction = 'auto';