Insertion in binary search tree using recursion in golang

Go program for Insertion in binary search tree using recursion. Here more information.

package main
import "fmt"
// Go program for
// Insertion in binary search tree by using recursion
type TreeNode struct {
	data int
	left * TreeNode
	right * TreeNode
}
func getTreeNode(data int) * TreeNode {
	// return new TreeNode
	return &TreeNode {
		data,
		nil,
		nil,
	}
}
type BinarySearchTree struct {
	root * TreeNode
}
func getBinarySearchTree() * BinarySearchTree {
	// return new BinarySearchTree
	return &BinarySearchTree {
		nil,
	}
}
// Insert a node element
func(this BinarySearchTree) addNode(node * TreeNode, 
	data int) * TreeNode {
	if node != nil {
		if node.data >= data {
			// When new element is smaller or
			// equal to current node
			node.left = this.addNode(node.left, data)
		} else {
			// When new element is higher to current node
			node.right = this.addNode(node.right, data)
		}
		// important to manage root node
		return node
	} else {
		return getTreeNode(data)
	}
}
// Display preorder
func(this BinarySearchTree) preorder(node * TreeNode) {
	if node != nil {
		// Display node value
		fmt.Print("  ", node.data)
		// Visit to left subtree
		this.preorder(node.left)
		// Visit to right subtree
		this.preorder(node.right)
	}
}
func(this BinarySearchTree) inorder(node * TreeNode) {
	if node != nil {
		// Visit to left subtree
		this.inorder(node.left)
		// Display node value
		fmt.Print("  ", node.data)
		// Visit to right subtree
		this.inorder(node.right)
	}
}
func(this BinarySearchTree) postorder(node * TreeNode) {
	if node != nil {
		// Visit to left subtree
		this.postorder(node.left)
		// Visit to right subtree
		this.postorder(node.right)
		// Display node value
		fmt.Print("  ", node.data)
	}
}
func main() {
	var tree * BinarySearchTree = getBinarySearchTree()
	/*
	         10
	        / \
	       /   \
	      4     15
	     / \   /
	    3   5 12
	    -------------
	    Build binary search tree


	*/
	tree.root = tree.addNode(tree.root, 10)
	tree.addNode(tree.root, 4)
	tree.addNode(tree.root, 3)
	tree.addNode(tree.root, 5)
	tree.addNode(tree.root, 15)
	tree.addNode(tree.root, 12)
	// Display tree nodes
	fmt.Println("Preorder ")
	tree.preorder(tree.root)
	fmt.Println("\nInorder ")
	tree.inorder(tree.root)
	fmt.Println("\nPostorder ")
	tree.postorder(tree.root)
}

Output

Preorder 
  10  4  3  5  15  12
Inorder 
  3  4  5  10  12  15
Postorder 
  3  5  4  12  15  10