diff --git a/archive_tree.libraries.yml b/archive_tree.libraries.yml
index b6823db..58817bf 100644
--- a/archive_tree.libraries.yml
+++ b/archive_tree.libraries.yml
@@ -3,3 +3,5 @@ archive_tree_styles:
   css:
     theme:
       css/archive_tree.css: {}
+  js:
+    js/archive_tree.js: {}
diff --git a/js/archive_tree.js b/js/archive_tree.js
new file mode 100644
index 0000000..42d1cd9
--- /dev/null
+++ b/js/archive_tree.js
@@ -0,0 +1,22 @@
+(function () {
+  // Wait for DOM ready
+  document.addEventListener('DOMContentLoaded', function () {
+    document.querySelectorAll('.archive-tree-year').forEach(function (summary) {
+      var details = summary.parentElement;
+      var year = summary.querySelector('a')?.textContent?.trim();
+      if (!year) return;
+      var key = 'archive_tree_year_' + year;
+      // Restore state
+      var open = localStorage.getItem(key);
+      if (open === 'true') {
+        details.setAttribute('open', '');
+      } else if (open === 'false') {
+        details.removeAttribute('open');
+      }
+      // Listen for toggle
+      details.addEventListener('toggle', function () {
+        localStorage.setItem(key, details.open ? 'true' : 'false');
+      });
+    });
+  });
+})();
diff --git a/src/Plugin/Block/ArchiveTreeBlock.php b/src/Plugin/Block/ArchiveTreeBlock.php
index f57c250..d9b9ae3 100644
--- a/src/Plugin/Block/ArchiveTreeBlock.php
+++ b/src/Plugin/Block/ArchiveTreeBlock.php
@@ -12,18 +12,42 @@ use Drupal\Core\Block\BlockBase;
  *   admin_label = @Translation("Archive tree"),
  * )
  */
+use Drupal\Core\Block\BlockForm;
+use Drupal\Core\Form\FormStateInterface;
+
 class ArchiveTreeBlock extends BlockBase {
   /**
    * {@inheritdoc}
    */
+  public function defaultConfiguration() {
+    return [
+      'expand_years' => FALSE,
+    ] + parent::defaultConfiguration();
+  }
+
+  public function blockForm($form, FormStateInterface $form_state) {
+    $form = parent::blockForm($form, $form_state);
+    $form['expand_years'] = [
+      '#type' => 'checkbox',
+      '#title' => $this->t('Expand all years by default'),
+      '#default_value' => $this->configuration['expand_years'],
+      '#description' => $this->t('If checked, all years will be expanded by default.'),
+    ];
+    return $form;
+  }
+
+  public function blockSubmit($form, FormStateInterface $form_state) {
+    parent::blockSubmit($form, $form_state);
+    $this->configuration['expand_years'] = $form_state->getValue('expand_years');
+  }
+
   public function build() {
     $storage = \Drupal::entityTypeManager()->getStorage('node');
     $query = $storage->getQuery()
       ->condition('type', 'article')
       ->condition('status', 1)
       ->sort('created', 'DESC')
-      ->accessCheck(TRUE)
-      ->addTag('DANGEROUS_ACCESS_CHECK_OPT_OUT');
+      ->accessCheck(TRUE);
     $nids = $query->execute();
     $nodes = $storage->loadMultiple($nids);
 
@@ -48,9 +72,11 @@ class ArchiveTreeBlock extends BlockBase {
     }
 
     $output = '';
+    $expand = !empty($this->configuration['expand_years']);
     foreach ($tree as $year => $data) {
       $year_url = '/archive-tree/' . $year;
-      $output .= '<details><summary class="archive-tree-year">';
+      $open = $expand ? ' open' : '';
+      $output .= '<details' . $open . '><summary class="archive-tree-year">';
       $output .= '<a href="' . $year_url . '">' . $year . '</a> (' . $data['count'] . ')';
       $output .= '</summary>';
       foreach ($data['months'] as $month => $count) {