diff -r 4b325b639117 -r 1f636de4a63f src/tree.c
--- a/src/tree.c	Mon Aug 19 18:46:49 2024 +0200
+++ b/src/tree.c	Mon Aug 19 20:46:36 2024 +0200
@@ -40,6 +40,26 @@
 #define tree_prev(node) CX_TREE_PTR(node, loc_prev)
 #define tree_next(node) CX_TREE_PTR(node, loc_next)
 
+#define cx_tree_ptr_locations \
+    loc_parent, loc_children, loc_last_child, loc_prev, loc_next
+
+static void cx_tree_zero_pointers(
+        void *node,
+        ptrdiff_t loc_parent,
+        ptrdiff_t loc_children,
+        ptrdiff_t loc_last_child,
+        ptrdiff_t loc_prev,
+        ptrdiff_t loc_next
+) {
+    tree_parent(node) = NULL;
+    tree_prev(node) = NULL;
+    tree_next(node) = NULL;
+    tree_children(node) = NULL;
+    if (loc_last_child >= 0) {
+        tree_last_child(node) = NULL;
+    }
+}
+
 void cx_tree_link(
         void *restrict parent,
         void *restrict node,
@@ -52,8 +72,7 @@
     void *current_parent = tree_parent(node);
     if (current_parent == parent) return;
     if (current_parent != NULL) {
-        cx_tree_unlink(node, loc_parent, loc_children, loc_last_child,
-                       loc_prev, loc_next);
+        cx_tree_unlink(node, cx_tree_ptr_locations);
     }
 
     if (tree_children(parent) == NULL) {
@@ -438,8 +457,50 @@
         ptrdiff_t loc_prev,
         ptrdiff_t loc_next
 ) {
-    // TODO: implement
-    return NULL;
+    if (*root == NULL) {
+        void *node = cfunc(src, NULL, cdata);
+        if (node == NULL) return NULL;
+        cx_tree_zero_pointers(node, cx_tree_ptr_locations);
+        *root = node;
+        return node;
+    }
+
+    void *match = NULL;
+    int result = cx_tree_search(
+            *root,
+            src,
+            sfunc,
+            &match,
+            loc_children,
+            loc_next
+    );
+
+    void *node;
+    if (result < 0) {
+        // new node is created as new parent
+        node = cfunc(src, NULL, cdata);
+        if (node == NULL) return NULL;
+        cx_tree_zero_pointers(node, cx_tree_ptr_locations);
+        cx_tree_link(node, *root, cx_tree_ptr_locations);
+        *root = node;
+        return node;
+    } else if (result == 0) {
+        // data already found in the tree, let cfunc decide
+        node = cfunc(src, match, cdata);
+        if (node == NULL) return NULL;
+        if (node != match) {
+            cx_tree_zero_pointers(node, cx_tree_ptr_locations);
+            cx_tree_link(match, node, cx_tree_ptr_locations);
+        }
+    } else {
+        // closest match found, add new node as child
+        node = cfunc(src, NULL, cdata);
+        if (node == NULL) return NULL;
+        cx_tree_zero_pointers(node, cx_tree_ptr_locations);
+        cx_tree_link(match, node, cx_tree_ptr_locations);
+    }
+
+    return node;
 }
 
 unsigned int cx_tree_add_look_around_depth = 3;
@@ -456,8 +517,87 @@
         ptrdiff_t loc_prev,
         ptrdiff_t loc_next
 ) {
-    // TODO: implement
-    return 0;
+    size_t processed = 0;
+    void *current_node = *root;
+    for (void **eptr;
+         iter->valid(iter) && (eptr = iter->current(iter)) != NULL;
+         iter->next(iter)) {
+        void *elem = *eptr;
+
+        if (current_node == NULL) {
+            // no node in tree, yet - add a new one
+            current_node = cfunc(elem, NULL, cdata);
+            // node creation failed - stop processing
+            if (current_node == NULL) {
+                // but honestly... nothing should have been processed
+                assert(processed == 0);
+                return 0;
+            }
+            cx_tree_zero_pointers(current_node, cx_tree_ptr_locations);
+            *root = current_node;
+            processed++;
+            continue;
+        }
+
+        // start searching from current node
+        void *match;
+        int result;
+        unsigned int look_around_retries = cx_tree_add_look_around_depth;
+        cx_tree_add_look_around_retry:
+        result = cx_tree_search(
+                current_node,
+                elem,
+                sfunc,
+                &match,
+                loc_children,
+                loc_next
+        );
+
+        void *node;
+        if (result < 0) {
+            // traverse upwards and try to find better parents
+            void *parent = tree_parent(current_node);
+            if (parent != NULL) {
+                if (look_around_retries > 0) {
+                    look_around_retries--;
+                    current_node = parent;
+                } else {
+                    // look around retries exhausted, start from the root
+                    current_node = *root;
+                }
+                goto cx_tree_add_look_around_retry;
+            } else {
+                // no parents. so we (try to) create a new root node
+                void *new_root = cfunc(elem, NULL, cdata);
+                if (new_root == NULL) return processed;
+                cx_tree_zero_pointers(new_root, cx_tree_ptr_locations);
+                cx_tree_link(new_root, current_node, cx_tree_ptr_locations);
+                current_node = new_root;
+                *root = new_root;
+            }
+        } else if (result == 0) {
+            // data already found in the tree, let cfunc decide
+            node = cfunc(elem, match, cdata);
+            if (node == NULL) return processed;
+            if (node != match) {
+                cx_tree_zero_pointers(node, cx_tree_ptr_locations);
+                cx_tree_link(match, node, cx_tree_ptr_locations);
+            }
+            current_node = node;
+        } else {
+            // closest match found, add new node as child
+            node = cfunc(elem, NULL, cdata);
+            if (node == NULL) return processed;
+            cx_tree_zero_pointers(node, cx_tree_ptr_locations);
+            cx_tree_link(match, node, cx_tree_ptr_locations);
+            // but make the match current and not the new node
+            // (usually saves one traversal when a lot of siblings are added)
+            current_node = match;
+        }
+
+        processed++;
+    }
+    return processed;
 }
 
 size_t cx_tree_add_array(