GoLang Binary Tree - using Interface and Struct

I am trying to use Interfaces and Struct in GoLang to create a binary tree concept

I wrote the below code

package main
import "fmt"
type node interface {
	add(a int)
	getval() int
}
type node_element struct {
	element int
	left  *node
	right *node
}
func (c *node_element) add(a int) {
	c.element = a
}
func (c *node_element) getval() int {
	return c.element
}
func main() {
	var s node
	s = &node_element{}
	s.add(1)
	fmt.Println(s.getval())
}

Now how do I instantiate left and right. I am using VIM with Go autocomplete. In auto complete on pressing . there is no list. Which means access to this pointer object to s is not happening

How to instantiate and use left and right ?

You don't need to declare s as a node, a *node_element can be used as a node. You also never want to have a pointer to an interface, so change the left and right types to node.

You can then just assign the fields directly:

s := &node_element{}
s.add(1)
s.left = &node_element{element: 2}
s.right = &node_element{element: 3}