diff --git a/codes/go/pkg/tree_node.go b/codes/go/pkg/tree_node.go
index 571dfac..6175688 100644
--- a/codes/go/pkg/tree_node.go
+++ b/codes/go/pkg/tree_node.go
@@ -9,6 +9,9 @@ import (
 	"fmt"
 )
 
+// nodeNotExist represents node don't exist.
+const nodeNotExist int = -1
+
 type TreeNode struct {
 	Val   int
 	Left  *TreeNode
@@ -55,7 +58,7 @@ func TreeToArray(root *TreeNode) []int {
 	if root == nil {
 		return []int{}
 	}
-	arr := make([]int, 16)
+	arr := make([]int, 0)
 	queue := list.New()
 	queue.PushBack(root)
 	for queue.Len() > 0 {
@@ -65,7 +68,7 @@ func TreeToArray(root *TreeNode) []int {
 			queue.PushBack(node.Left)
 			queue.PushBack(node.Right)
 		} else {
-			arr = append(arr, -1)
+			arr = append(arr, nodeNotExist)
 		}
 	}
 	return arr
@@ -73,19 +76,19 @@ func TreeToArray(root *TreeNode) []int {
 
 // PrintTree Print a binary tree
 func PrintTree(root *TreeNode) {
-	PrintTreeHelper(root, nil, false)
+	printTreeHelper(root, nil, false)
 }
 
-// PrintTreeHelper Help to print a binary tree, hide more details
+// printTreeHelper Help to print a binary tree, hide more details
 // This tree printer is borrowed from TECHIE DELIGHT
 // https://www.techiedelight.com/c-program-print-binary-tree/
-func PrintTreeHelper(root *TreeNode, prev *trunk, isLeft bool) {
+func printTreeHelper(root *TreeNode, prev *trunk, isLeft bool) {
 	if root == nil {
 		return
 	}
 	prevStr := "    "
 	trunk := newTrunk(prev, prevStr)
-	PrintTreeHelper(root.Right, trunk, true)
+	printTreeHelper(root.Right, trunk, true)
 	if prev == nil {
 		trunk.str = "———"
 	} else if isLeft {
@@ -101,7 +104,7 @@ func PrintTreeHelper(root *TreeNode, prev *trunk, isLeft bool) {
 		prev.str = prevStr
 	}
 	trunk.str = "   |"
-	PrintTreeHelper(root.Left, trunk, false)
+	printTreeHelper(root.Left, trunk, false)
 }
 
 // trunk Help to Print tree structure
diff --git a/codes/go/pkg/tree_node_test.go b/codes/go/pkg/tree_node_test.go
index c761ecb..ffbdf6f 100644
--- a/codes/go/pkg/tree_node_test.go
+++ b/codes/go/pkg/tree_node_test.go
@@ -12,4 +12,7 @@ func TestTreeNode(t *testing.T) {
 
 	// print tree
 	PrintTree(node)
+
+	// tree to arr
+	t.Log(TreeToArray(node))
 }