diff --git a/rootfs/rootfs.go b/rootfs/rootfs.go
index ea4cb73..5028ea8 100644
--- a/rootfs/rootfs.go
+++ b/rootfs/rootfs.go
@@ -193,10 +193,10 @@ func writeFile(tr *tar.Reader, tw *tar.Writer, hdr *tar.Header) error {
 	return nil
 }
 
-func whiteoutDirs(whreaddir map[string]int, nlayers int) []*Tree {
-	ret := make([]*Tree, nlayers)
+func whiteoutDirs(whreaddir map[string]int, nlayers int) []*tree {
+	ret := make([]*tree, nlayers)
 	for i := range ret {
-		ret[i] = New()
+		ret[i] = newTree()
 	}
 	for fname, layer := range whreaddir {
 		if layer == 0 {
diff --git a/rootfs/tree.go b/rootfs/tree.go
index 06d9bce..6c7a7a0 100644
--- a/rootfs/tree.go
+++ b/rootfs/tree.go
@@ -6,18 +6,18 @@ import (
 	"strings"
 )
 
-// Tree is a way to store directory paths for whiteouts.
+// tree is a way to store directory paths for whiteouts.
 // It is semi-optimized for reads and non-optimized for writes;
 // See Merge() and HasPrefix for trade-offs.
-type Tree struct {
+type tree struct {
 	name     string
-	children []*Tree
+	children []*tree
 	end      bool
 }
 
 // New creates a new tree from a given path.
-func New(paths ...string) *Tree {
-	t := &Tree{name: ".", children: []*Tree{}}
+func newTree(paths ...string) *tree {
+	t := &tree{name: ".", children: []*tree{}}
 	for _, path := range paths {
 		t.Add(path)
 	}
@@ -25,7 +25,7 @@ func New(paths ...string) *Tree {
 }
 
 // Add adds a sequence to a tree
-func (t *Tree) Add(path string) {
+func (t *tree) Add(path string) {
 	t.add(strings.Split(filepath.Clean(path), "/"))
 }
 
@@ -35,18 +35,18 @@ func (t *Tree) Add(path string) {
 // really small (usually 1 or 2), it does not really matter. If you find a
 // real-world container with 30+ whiteout paths on a single path, please ping
 // the author/maintainer of this code.
-func (t *Tree) HasPrefix(path string) bool {
+func (t *tree) HasPrefix(path string) bool {
 	return t.hasprefix(strings.Split(filepath.Clean(path), "/"))
 }
 
 // Merge merges adds t2 to t. It is not optimized for speed, since it's walking
 // full branch for every other branch.
-func (t *Tree) Merge(t2 *Tree) {
+func (t *tree) Merge(t2 *tree) {
 	t.merge(t2, []string{})
 }
 
 // String stringifies a tree
-func (t *Tree) String() string {
+func (t *tree) String() string {
 	if len(t.children) == 0 {
 		return "<empty>"
 	}
@@ -57,7 +57,7 @@ func (t *Tree) String() string {
 	return strings.Join(res.res, ":")
 }
 
-func (t *Tree) add(nodes []string) {
+func (t *tree) add(nodes []string) {
 	if len(nodes) == 0 {
 		t.end = true
 		return
@@ -69,12 +69,12 @@ func (t *Tree) add(nodes []string) {
 		}
 	}
 
-	newNode := &Tree{name: nodes[0]}
+	newNode := &tree{name: nodes[0]}
 	t.children = append(t.children, newNode)
 	newNode.add(nodes[1:])
 }
 
-func (t *Tree) hasprefix(nodes []string) bool {
+func (t *tree) hasprefix(nodes []string) bool {
 	if len(nodes) == 0 {
 		return t.end
 	}
@@ -95,7 +95,7 @@ type stringer struct {
 	res []string
 }
 
-func (s *stringer) stringify(t *Tree, acc []string) {
+func (s *stringer) stringify(t *tree, acc []string) {
 	if t.name == "" {
 		return
 	}
@@ -109,7 +109,7 @@ func (s *stringer) stringify(t *Tree, acc []string) {
 	}
 }
 
-func (t *Tree) merge(t2 *Tree, acc []string) {
+func (t *tree) merge(t2 *tree, acc []string) {
 	if t2.end {
 		t.add(append(acc[1:], t2.name))
 	}
diff --git a/rootfs/tree_test.go b/rootfs/tree_test.go
index 4b44af8..5cab76d 100644
--- a/rootfs/tree_test.go
+++ b/rootfs/tree_test.go
@@ -33,7 +33,7 @@ func TestTree(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			tree := New(tt.paths...)
+			tree := newTree(tt.paths...)
 
 			for _, path := range tt.matchTrue {
 				t.Run(path, func(t *testing.T) {
@@ -53,8 +53,8 @@ func TestTree(t *testing.T) {
 }
 
 func TestTreeMerge(t *testing.T) {
-	tree1 := New("bin/ar", "var/cache/apt")
-	tree2 := New("bin/ar", "bin/busybox", "usr/share/doc")
+	tree1 := newTree("bin/ar", "var/cache/apt")
+	tree2 := newTree("bin/ar", "bin/busybox", "usr/share/doc")
 	tree1.Merge(tree2)
 	assert.Equal(t, "./bin/ar:./bin/busybox:./usr/share/doc:./var/cache/apt", tree1.String())
 	assert.Equal(t, "./bin/ar:./bin/busybox:./usr/share/doc", tree2.String())
@@ -90,7 +90,7 @@ func TestString(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			tree := New(tt.paths...)
+			tree := newTree(tt.paths...)
 			assert.Equal(t, tt.wantStr, tree.String())
 		})
 	}