Utils: Fix propagation of underlying tree model

Change-Id: I23739cb4c7a19a5c5bcdc8bf39c36db689292b62
Reviewed-by: hjk <hjk@theqtcompany.com>

src/libs/utils/treemodel.cpp

@@ -705,6 +705,8 @@ void TreeItem::insertChild(int pos, TreeItem *item)
         m_model->endInsertRows();
     } else {
         item->m_parent = this;
+        if (m_model)
+            item->propagateModel(m_model);
         m_children.insert(m_children.begin() + pos, item);
     }
 }