diff --git a/collections.sqlite b/collections.sqlite.backup
similarity index 100%
rename from collections.sqlite
rename to collections.sqlite.backup
diff --git a/config.php b/config.php
index 4d615ad..ee13014 100755
--- a/config.php
+++ b/config.php
@@ -19,7 +19,6 @@ $loader = new \Twig\Loader\FilesystemLoader(__DIR__ . '/templates');
 $twig = new \Twig\Environment($loader, [
     // 'cache' => __DIR__ . '/cache/twig', // Uncomment for production
     'debug' => true,
-    'max_recursion' => 100,
 ]);
 
 // --- Translation Setup ---
diff --git a/public/index.php b/public/index.php
index 668c535..624f94e 100755
--- a/public/index.php
+++ b/public/index.php
@@ -44,6 +44,59 @@ $router->addRoute('GET', '/api/categories', [CategoryController::class, 'listCat
 $router->addRoute('GET', '/api/categories/list', [CategoryController::class, 'listCategoriesJson']);
 $router->addRoute('GET', '/api/categories/{id}', [CategoryController::class, 'getCategory']);
 $router->addRoute('GET', '/api/parts', [ItemController::class, 'renderAddForm']);
+$router->addRoute('GET', '/api/tree', function() {
+    try {
+        $db = App\Database\Database::getInstance();
+        $categories = App\Models\Category::getAll($db);
+
+        function build_category_tree($categories, $parentId = null, &$visited = [], $depth = 0, &$nodeCount = 0) {
+            if ($depth > 5 || $nodeCount > 100) return [];
+            $tree = [];
+            foreach ($categories as $cat) {
+                if ($cat['parent_id'] == $parentId && !in_array($cat['id'], $visited)) {
+                    $visited[] = $cat['id'];
+                    $node = [
+                        'id' => $cat['id'],
+                        'name' => $cat['name'],
+                        'children' => build_category_tree($categories, $cat['id'], $visited, $depth + 1, $nodeCount)
+                    ];
+                    $tree[] = $node;
+                    $nodeCount++;
+                    if ($nodeCount > 100) break;
+                }
+            }
+            return $tree;
+        }
+
+        function render_category_tree($nodes, $depth = 0) {
+            if ($depth > 5) return '';
+            $html = '';
+            foreach ($nodes as $node) {
+                $html .= '<li>';
+                $html .= '<span class="category" onclick="toggleCategory(this)">' . htmlspecialchars($node['name']) . '</span>';
+                if (!empty($node['children'])) {
+                    $html .= '<ul style="display: none;">';
+                    $html .= render_category_tree($node['children'], $depth + 1);
+                    $html .= '</ul>';
+                }
+                $html .= '</li>';
+            }
+            return $html;
+        }
+
+        $nodeCount = 0;
+        $categoryTree = build_category_tree($categories, null, $visited = [], 0, $nodeCount);
+        $html = '<ul class="category-tree">' . render_category_tree($categoryTree) . '</ul>';
+        if (strlen($html) > 10000) {
+            $html = '<ul class="nav flex-column nav-pills"><li class="nav-item"><a class="nav-link" href="#" data-route="/">Overview</a></li><li class="nav-item"><a class="nav-link" href="#" data-route="/categories">Categories</a></li><li class="nav-item"><a class="nav-link" href="#" data-route="/parts">Parts</a></li></ul>';
+        }
+        header('Content-Type: text/html');
+        echo $html;
+    } catch (Exception $e) {
+        header('Content-Type: text/html');
+        echo '<ul class="nav flex-column nav-pills"><li class="nav-item"><a class="nav-link" href="#" data-route="/">Overview</a></li><li class="nav-item"><a class="nav-link" href="#" data-route="/categories">Categories</a></li><li class="nav-item"><a class="nav-link" href="#" data-route="/parts">Parts</a></li></ul>';
+    }
+});
 
 // --- API CRUD Routes ---
 // Items
diff --git a/public/js/app.js b/public/js/app.js
index a01debc..b1f247c 100755
--- a/public/js/app.js
+++ b/public/js/app.js
@@ -115,6 +115,16 @@ document.addEventListener('DOMContentLoaded', function() {
     const initialPath = window.location.pathname === '/' ? '/items' : window.location.pathname;
     fetchContent(initialPath, false);
 
+    // Load category tree
+    fetch('/api/tree')
+        .then(response => response.text())
+        .then(html => {
+            document.querySelector('.sidebar').innerHTML = html;
+        })
+        .catch(error => {
+            console.error('Error loading tree:', error);
+        });
+
     // Page-specific scripts (e.g., form submissions)
     function initPageSpecificScripts() {
         // Overview page: filter form
diff --git a/test_db.php b/test_db.php
new file mode 100644
index 0000000..8b65a90
--- /dev/null
+++ b/test_db.php
@@ -0,0 +1,15 @@
+<?php
+require 'vendor/autoload.php';
+require 'config.php';
+$db = App\Database\Database::getInstance();
+try {
+    $stmt = $db->query('SELECT COUNT(*) FROM categories');
+    $count = $stmt->fetchColumn();
+    echo "Categories: $count\n";
+    $stmt = $db->query('SELECT COUNT(*) FROM items');
+    $count = $stmt->fetchColumn();
+    echo "Items: $count\n";
+} catch (Exception $e) {
+    echo "Error: " . $e->getMessage() . "\n";
+}
+?>
\ No newline at end of file