ONOS-5552 DocumentTree builder not available

Change-Id: Id0e9e0c647146c27e21e2ec2b2014789bbd9eca9
diff --git a/core/api/src/main/java/org/onosproject/store/service/StorageService.java b/core/api/src/main/java/org/onosproject/store/service/StorageService.java
index 2e2acfb..21fdfda 100644
--- a/core/api/src/main/java/org/onosproject/store/service/StorageService.java
+++ b/core/api/src/main/java/org/onosproject/store/service/StorageService.java
@@ -44,6 +44,14 @@
     <K, V> ConsistentMapBuilder<K, V> consistentMapBuilder();
 
     /**
+     * Creates a new ConsistentMapBuilder.
+     *
+     * @param <V> value type
+     * @return builder for a consistent map
+     */
+    <V> DocumentTreeBuilder<V> documentTreeBuilder();
+
+    /**
      * Creates a new {@code AsyncConsistentTreeMapBuilder}.
      *
      * @param <V> value type