diff --git a/trie2/trie2.go b/trie2/trie2.go
index ec36b33..a8c9230 100644
--- a/trie2/trie2.go
+++ b/trie2/trie2.go
@@ -23,6 +23,7 @@ func (dt *DTrie[T]) Put(k string, v T) {
 		dt.values = append(dt.values, v)
 		return
 	}
+	// update an existed value.
 	dt.values[id-1] = v
 }
 
@@ -44,7 +45,7 @@ func (dt *DTrie[T]) Freeze(copyValues bool) *STrie[T] {
 	tree := trietree.Freeze(&dt.tree)
 	var values []T
 	if copyValues {
-		values = make([]T, len(values))
+		values = make([]T, len(dt.values))
 		copy(values, dt.values)
 	} else {
 		values = dt.values
@@ -52,20 +53,26 @@ func (dt *DTrie[T]) Freeze(copyValues bool) *STrie[T] {
 	return &STrie[T]{tree: *tree, values: values}
 }
 
-func (st *STrie[T]) Marshal(w io.Writer) error {
+func (st *STrie[T]) Marshal(w io.Writer, marshalValues func(io.Writer, []T) error) error {
 	if len(st.values) != len(st.tree.Levels) {
 		return fmt.Errorf("number of values and levels unmatched: value=%d levels=%d", len(st.values), len(st.tree.Levels))
 	}
 	if err := st.tree.Write(w); err != nil {
 		return err
 	}
+	if marshalValues != nil {
+		if err := marshalValues(w, st.values); err != nil {
+			return fmt.Errorf("failed to marshal values: %w", err)
+		}
+		return nil
+	}
 	if err := gob.NewEncoder(w).Encode(st.values); err != nil {
 		return err
 	}
 	return nil
 }
 
-func Unmarshal[T any](r io.Reader) (*STrie[T], error) {
+func Unmarshal[T any](r io.Reader, unmarshalValues func(io.Reader, int) ([]T, error)) (*STrie[T], error) {
 	tree, err := trietree.Read(r)
 	if err != nil {
 		return nil, err
@@ -73,7 +80,15 @@ func Unmarshal[T any](r io.Reader) (*STrie[T], error) {
 	if len(tree.Levels) == 0 {
 		return &STrie[T]{tree: *tree}, nil
 	}
-	// read v from r then append it to values.
+	// read values from r with unmarshalValues.
+	if unmarshalValues != nil {
+		values, err := unmarshalValues(r, len(tree.Levels))
+		if err != nil {
+			return nil, err
+		}
+		return &STrie[T]{tree: *tree, values: values}, nil
+	}
+	// read values from r without unmarshalValues.
 	values := make([]T, 0, len(tree.Levels))
 	if err := gob.NewDecoder(r).Decode(&values); err != nil {
 		return nil, err
diff --git a/trie2/trie2_test.go b/trie2/trie2_test.go
new file mode 100644
index 0000000..bb88115
--- /dev/null
+++ b/trie2/trie2_test.go
@@ -0,0 +1,169 @@
+package trie2
+
+import (
+	"bytes"
+	"encoding/json"
+	"io"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+type Data struct {
+	N int
+	S string
+}
+
+func TestMarshal0(t *testing.T) {
+	dt := DTrie[Data]{}
+	bb := &bytes.Buffer{}
+	if err := dt.Freeze(false).Marshal(bb, nil); err != nil {
+		t.Fatalf("failed to marshal: %s", err)
+	}
+	st, err := Unmarshal[Data](bb, nil)
+	if err != nil {
+		t.Fatalf("failed to unmarshal: %s", err)
+	}
+	if d := cmp.Diff(dt.values, st.values); d != "" {
+		t.Errorf("failed unmarshal values: -want +got\n%s", d)
+	}
+}
+
+func TestMarshalValue(t *testing.T) {
+	dt := DTrie[Data]{}
+	dt.Put("a", Data{111, "aaa"})
+	dt.Put("ab", Data{222, "bbb"})
+	dt.Put("abc", Data{333, "ccc"})
+	dt.Put("d", Data{444, "ddd"})
+	dt.Put("de", Data{555, "eee"})
+	bb := &bytes.Buffer{}
+	if err := dt.Freeze(false).Marshal(bb, nil); err != nil {
+		t.Fatalf("failed to marshal: %s", err)
+	}
+	st, err := Unmarshal[Data](bb, nil)
+	if err != nil {
+		t.Fatalf("failed to unmarshal: %s", err)
+	}
+	if d := cmp.Diff(dt.values, st.values); d != "" {
+		t.Errorf("failed unmarshal values: -want +got\n%s", d)
+	}
+}
+
+func TestMarshalPointer(t *testing.T) {
+	dt := DTrie[*Data]{}
+	dt.Put("a", &Data{111, "aaa"})
+	dt.Put("ab", &Data{222, "bbb"})
+	dt.Put("abc", &Data{333, "ccc"})
+	dt.Put("d", &Data{444, "ddd"})
+	dt.Put("de", &Data{555, "eee"})
+	bb := &bytes.Buffer{}
+	if err := dt.Freeze(false).Marshal(bb, nil); err != nil {
+		t.Fatalf("failed to marshal: %s", err)
+	}
+	st, err := Unmarshal[*Data](bb, nil)
+	if err != nil {
+		t.Fatalf("failed to unmarshal: %s", err)
+	}
+	if d := cmp.Diff(dt.values, st.values); d != "" {
+		t.Errorf("failed unmarshal values: -want +got\n%s", d)
+	}
+}
+
+type DataJSON struct {
+	N int    `json:"n"`
+	S string `json:"s"`
+}
+
+func TestMarshalCustom(t *testing.T) {
+	dt := DTrie[DataJSON]{}
+	dt.Put("a", DataJSON{111, "aaa"})
+	dt.Put("ab", DataJSON{222, "bbb"})
+	dt.Put("abc", DataJSON{333, "ccc"})
+	dt.Put("d", DataJSON{444, "ddd"})
+	dt.Put("de", DataJSON{555, "eee"})
+	bb := &bytes.Buffer{}
+	err := dt.Freeze(true).Marshal(bb, func(w io.Writer, values []DataJSON) error {
+		return json.NewEncoder(w).Encode(values)
+	})
+	if err != nil {
+		t.Fatalf("failed to marshal: %s", err)
+	}
+	st, err := Unmarshal[DataJSON](bb, func(r io.Reader, n int) ([]DataJSON, error) {
+		values := make([]DataJSON, 0, n)
+		if err := json.NewDecoder(r).Decode(&values); err != nil {
+			return nil, err
+		}
+		return values, nil
+	})
+	if err != nil {
+		t.Fatalf("failed to unmarshal: %s", err)
+	}
+	if d := cmp.Diff(dt.values, st.values); d != "" {
+		t.Errorf("failed unmarshal values: -want +got\n%s", d)
+	}
+}
+
+func TestLongestPrefixDTree(t *testing.T) {
+	dt := DTrie[Data]{}
+	dt.Put("a", Data{111, "aaa"})
+	dt.Put("ab", Data{222, "bbb"})
+	dt.Put("abc", Data{333, "ccc"})
+	dt.Put("d", Data{444, "ddd"})
+	dt.Put("de", Data{555, "eee"})
+	for i, c := range []struct {
+		query string
+		wantV Data
+		wantP string
+		wantF bool
+	}{
+		{"az", Data{111, "aaa"}, "a", true},
+		{"za", Data{}, "", false},
+		{"abcde", Data{333, "ccc"}, "abc", true},
+		{"ababc", Data{222, "bbb"}, "ab", true},
+	} {
+		gotV, gotP, gotF := dt.LongestPrefix(c.query)
+		if gotF != c.wantF {
+			t.Errorf("existence unmatch #%d: want=%t got=%t", i, c.wantF, gotF)
+			continue
+		}
+		if gotP != c.wantP {
+			t.Errorf("prefix unmatch #%d: want=%s got=%s", i, c.wantP, gotP)
+		}
+		if d := cmp.Diff(c.wantV, gotV); d != "" {
+			t.Errorf("values unmatch #%d: -want +got\n%s", i, d)
+		}
+	}
+}
+
+func TestLongestPrefixSTree(t *testing.T) {
+	dt := DTrie[Data]{}
+	dt.Put("a", Data{111, "aaa"})
+	dt.Put("ab", Data{222, "bbb"})
+	dt.Put("abc", Data{333, "ccc"})
+	dt.Put("d", Data{444, "ddd"})
+	dt.Put("de", Data{555, "eee"})
+	st := dt.Freeze(false)
+	for i, c := range []struct {
+		query string
+		wantV Data
+		wantP string
+		wantF bool
+	}{
+		{"az", Data{111, "aaa"}, "a", true},
+		{"za", Data{}, "", false},
+		{"abcde", Data{333, "ccc"}, "abc", true},
+		{"ababc", Data{222, "bbb"}, "ab", true},
+	} {
+		gotV, gotP, gotF := st.LongestPrefix(c.query)
+		if gotF != c.wantF {
+			t.Errorf("existence unmatch #%d: want=%t got=%t", i, c.wantF, gotF)
+			continue
+		}
+		if gotP != c.wantP {
+			t.Errorf("prefix unmatch #%d: want=%s got=%s", i, c.wantP, gotP)
+		}
+		if d := cmp.Diff(c.wantV, gotV); d != "" {
+			t.Errorf("values unmatch #%d: -want +got\n%s", i, d)
+		}
+	}
+}