diff --git a/treevalue/tree/tree/tree.pxd b/treevalue/tree/tree/tree.pxd
index c034b1e06577c05d103ad6590a19db15fd181719..53e9ec5d846a0ea19389e876a34de680d05bbc38 100644
--- a/treevalue/tree/tree/tree.pxd
+++ b/treevalue/tree/tree/tree.pxd
@@ -3,6 +3,7 @@
 
 from libcpp cimport bool
 
+from .constraint cimport Constraint
 from ..common.delay cimport DelayedProxy
 from ..common.storage cimport TreeStorage
 
@@ -11,6 +12,7 @@ cdef class _CObject:
 
 cdef class TreeValue:
     cdef readonly TreeStorage _st
+    cdef readonly Constraint _constraint
     cdef readonly type _type
 
     cpdef TreeStorage _detach(self)
@@ -20,7 +22,7 @@ cdef class TreeValue:
     cpdef _getitem_extern(self, object key)
     cpdef _setitem_extern(self, object key, object value)
     cpdef _delitem_extern(self, object key)
-    cdef void _update(self, object d, dict kwargs) except *
+    cdef void _update(self, object d, dict kwargs) except*
     cpdef public get(self, str key, object default= *)
     cpdef public pop(self, str key, object default= *)
     cpdef public popitem(self)
diff --git a/treevalue/tree/tree/tree.pyx b/treevalue/tree/tree/tree.pyx
index 148fac32d3a3507ae89cdfd1700ef3dac7f75a4d..e63e6c1df0e198f4bbe48a6784e09719f7e5a366 100644
--- a/treevalue/tree/tree/tree.pyx
+++ b/treevalue/tree/tree/tree.pyx
@@ -8,6 +8,7 @@ from operator import itemgetter
 import cython
 from hbutils.design import SingletonMark
 
+from .constraint cimport Constraint, to_constraint, EmptyConstraint
 from ..common.delay cimport undelay, _c_delayed_partial, DelayedProxy
 from ..common.storage cimport TreeStorage, create_storage, _c_undelay_data
 from ...utils import format_tree
@@ -56,12 +57,13 @@ cdef class TreeValue:
         The `TreeValue` class is a light-weight framework just for DIY.
     """
 
-    def __cinit__(self, object data):
+    def __cinit__(self, object data, Constraint constraint=None):
         self._st = _DEFAULT_STORAGE
+        self._constraint = EmptyConstraint() if constraint is None else constraint
         self._type = type(self)
 
     @cython.binding(True)
-    def __init__(self, object data):
+    def __init__(self, object data, object constraint=None):
         """
         Constructor of :class:`TreeValue`.
 
@@ -100,6 +102,8 @@ cdef class TreeValue:
                 "Unknown initialization type for tree value - {type}.".format(
                     type=repr(type(data).__name__)))
 
+        self._constraint = to_constraint(constraint)
+
     def __getnewargs_ex__(self):  # for __cinit__, when pickle.loads
         return ({},), {}