diff -r 12315ee158ad -r 72ad8a78378a src/cx/tree.h
--- a/src/cx/tree.h	Sat Dec 06 17:51:08 2025 +0100
+++ b/src/cx/tree.h	Sat Dec 06 18:01:52 2025 +0100
@@ -643,17 +643,13 @@
  * Structure for holding the base data of a tree.
  */
 struct cx_tree_s {
+    CX_COLLECTION_BASE;
     /**
      * The tree class definition.
      */
     const cx_tree_class *cl;
 
     /**
-     * Allocator to allocate new nodes.
-     */
-    const CxAllocator *allocator;
-
-    /**
      * A pointer to the root node.
      *
      * Will be @c NULL when @c size is 0.
@@ -671,21 +667,6 @@
     cx_tree_node_create_func node_create;
 
     /**
-     * An optional simple destructor for the tree nodes.
-     */
-    cx_destructor_func simple_destructor;
-
-    /**
-     * An optional advanced destructor for the tree nodes.
-     */
-    cx_destructor_func2 advanced_destructor;
-
-    /**
-     * The pointer to additional data that is passed to the advanced destructor.
-     */
-    void *destructor_data;
-
-    /**
      * A function to compare two nodes.
      */
     cx_tree_search_func search;
@@ -696,11 +677,6 @@
     cx_tree_search_data_func search_data;
 
     /**
-     * The number of currently stored elements.
-     */
-    size_t size;
-
-    /**
      * Offset in the node struct for the parent pointer.
      */
     ptrdiff_t loc_parent;