diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -2148,6 +2148,19 @@
     # hook for extensions to execute code on the optimized tree
     pass
 
+def buildtree(specs, repo=None):
+    """ builds the tree on basis of specs and returns it """
+    lookup = None
+    if repo:
+        lookup = repo.__contains__
+    if len(specs) == 1:
+        tree = revsetlang.parse(specs[0], lookup)
+    else:
+        tree = ('or',
+                ('list',) + tuple(revsetlang.parse(s, lookup) for s in specs))
+
+    return tree
+
 def match(ui, spec, repo=None):
     """Create a matcher for a single revision spec"""
     return matchany(ui, [spec], repo=repo)
@@ -2167,14 +2180,8 @@
         return emptymatcher
     if not all(specs):
         raise error.ParseError(_("empty query"))
-    lookup = None
-    if repo:
-        lookup = repo.__contains__
-    if len(specs) == 1:
-        tree = revsetlang.parse(specs[0], lookup)
-    else:
-        tree = ('or',
-                ('list',) + tuple(revsetlang.parse(s, lookup) for s in specs))
+
+    tree = buildtree(specs, repo)
 
     aliases = []
     warn = None