gistfile1.txt

/*
    
    
    
        A
      /   \
     B     C
    / \   / \
   D   E F   G
*/


function Node(id, value, left, right) {
    this.id = id
    this.value = value
    this.left = left
    this.right = right
}

// the tree is constructed bottom up
// ie. rotate the above diagram 180 degrees

// left

const dNode = new Node('D', 'dup')
const eNode = new Node('E', 'dup')

const bNode = new Node('B', 'unique1', dNode, eNode)

// right

const fNode = new Node('F', 'unique2')
const gNode = new Node('G', 'unique3')

const cNode = new Node('B', 'unique4', fNode, gNode)

// root

const aNode = new Node('A', 'unique5', bNode, cNode);

const output = new Set();

function dfs(root){
  if(root === null) return

  output.add(root.value)

  if(root.left) dfs(root.left)
  if(root.right) dfs(root.right)
}

dfs(aNode)

console.log('> output', output); // should have all 'unique{X}', and one 'dup'