diff --git a/src/widgets/tree_widget.h b/src/widgets/tree_widget.h
new file mode 100644
--- /dev/null
+++ b/src/widgets/tree_widget.h
@@ -0,0 +1,33 @@
+/* $Id$ */
+
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file tree_widget.h Types related to the tree widgets. */
+
+#ifndef WIDGETS_TREE_WIDGET_H
+#define WIDGETS_TREE_WIDGET_H
+
+/** Widgets of the WC_BUILD_TREES. */
+enum BuildTreesWidgets {
+	BTW_TYPE_11,
+	BTW_TYPE_12,
+	BTW_TYPE_13,
+	BTW_TYPE_14,
+	BTW_TYPE_21,
+	BTW_TYPE_22,
+	BTW_TYPE_23,
+	BTW_TYPE_24,
+	BTW_TYPE_31,
+	BTW_TYPE_32,
+	BTW_TYPE_33,
+	BTW_TYPE_34,
+	BTW_TYPE_RANDOM,
+	BTW_MANY_RANDOM,
+};
+
+#endif /* WIDGETS_TREE_WIDGET_H */