Adding additional resources for instantiating async consistent treemaps.

Change-Id: I7bfc602ac22eda1844fea2a7b3e3133f83157bf3
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 e646e38..4edb438 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 {@code AsyncConsistentTreeMapBuilder}.
+     *
+     * @param <V> value type
+     * @return builder for a async consistent tree map
+     */
+    <V> ConsistentTreeMapBuilder<V> consistentTreeMapBuilder();
+
+    /**
      * Creates a new DistributedSetBuilder.
      *
      * @param <E> set element type