diff --git a/tree_json.go b/tree_json.go
index 47768db..74a1b3a 100644
--- a/tree_json.go
+++ b/tree_json.go
@@ -9,6 +9,11 @@ type jsonTree struct {
 	*tree
 }
 
+// noop
+func (jt *jsonTree) grow() error {
+	return nil
+}
+
 func (jt *jsonTree) spread(w io.Writer) error {
 	enc := json.NewEncoder(w)
 
diff --git a/tree_toml.go b/tree_toml.go
index 2334f46..e780e27 100644
--- a/tree_toml.go
+++ b/tree_toml.go
@@ -10,6 +10,11 @@ type tomlTree struct {
 	*tree
 }
 
+// noop
+func (tt *tomlTree) grow() error {
+	return nil
+}
+
 func (tt *tomlTree) spread(w io.Writer) error {
 	enc := toml.NewEncoder(w)
 
diff --git a/tree_yaml.go b/tree_yaml.go
index 4a5d454..2027ca7 100644
--- a/tree_yaml.go
+++ b/tree_yaml.go
@@ -10,6 +10,11 @@ type yamlTree struct {
 	*tree
 }
 
+// noop
+func (yt *yamlTree) grow() error {
+	return nil
+}
+
 func (yt *yamlTree) spread(w io.Writer) error {
 	enc := yaml.NewEncoder(w)