tree: When changing children of tree node, don't bother resorting chi…

…ldren if already sorted

src/crystal/ui/tree.py

@@ -301,10 +301,32 @@ def set_children(self,
                     for child in children_to_add:
                         child._attach(NodeViewPeer(self.peer._tree, self.peer.AppendItem('')))
 
-                    # Reorder children
-                    for (index, child) in enumerate(new_children):
-                        child._order_index = index  # type: ignore[attr-defined]
-                    self.peer.SortChildren()
+                    # Calculate whether needs_reorder
+                    last_order_index = -1
+                    for child in new_children:
+                        cur_order_index = getattr(child, '_order_index', None)
+                        if cur_order_index is None:
+                            if last_order_index != -1:
+                                # New child without order-index mixed with
+                                # old children with order-index
+                                needs_reorder = True
+                                break
+                            else:
+                                # New child without order-index mixed with
+                                # only other new children without order-index
+                                continue
+                        if cur_order_index < last_order_index:
+                            needs_reorder = True
+                            break
+                        last_order_index = cur_order_index
+                    else:
+                        needs_reorder = False
+
+                    if needs_reorder:
+                        # Reorder children
+                        for (index, child) in enumerate(new_children):
+                            child._order_index = index  # type: ignore[attr-defined]
+                        self.peer.SortChildren()
             except WindowDeletedError:
                 pass