diff --git a/README.md b/README.md
index d3b52f7..c527037 100644
--- a/README.md
+++ b/README.md
@@ -61,6 +61,9 @@ SelectTree::make('category_id')
 // Set nodes as dependent
 ->independent(false)
 
+// Set the parent's null value to -1, allowing you to use -1 as a sentinel value (default = null)
+->parentNullValue(-1)
+
 // Expand the tree with selected values
 ->expandSelected(false)
 
diff --git a/src/SelectTree.php b/src/SelectTree.php
index 7433fd2..8ce40ca 100644
--- a/src/SelectTree.php
+++ b/src/SelectTree.php
@@ -31,6 +31,8 @@ class SelectTree extends Field
 
     protected string $parentAttribute;
 
+    protected null|int|string $parentNullValue = null;
+
     protected bool $clearable = true;
 
     protected bool $expandSelected = true;
@@ -79,8 +81,11 @@ protected function setUp(): void
         });
     }
 
-    private function buildTree(int $parent = null): array|Collection
+    private function buildTree($parent = null): array|Collection
     {
+        // Assign the parent's null value to the $parent variable if it's not null
+        $parent = $this->getParentNullValue() ?? $parent;
+
         // Create a default query to retrieve related items.
         $defaultQuery = $this->getRelationship()
             ->getRelated()
@@ -134,6 +139,13 @@ public function direction(string $direction): static
         return $this;
     }
 
+    public function parentNullValue(int|string $parentNullValue = null): static
+    {
+        $this->parentNullValue = $parentNullValue;
+
+        return $this;
+    }
+
     public function getRelationship(): BelongsToMany|BelongsTo
     {
         return $this->getModelInstance()->{$this->evaluate($this->relationship)}();
@@ -149,6 +161,11 @@ public function getParentAttribute(): string
         return $this->evaluate($this->parentAttribute);
     }
 
+    public function getParentNullValue(): null|int|string
+    {
+        return $this->evaluate($this->parentNullValue);
+    }
+
     public function clearable(bool $clearable = true): static
     {
         $this->clearable = $clearable;