深度优先遍历

function deep(tree, callback) {
  const queue = [tree]

  while (queue.length) {
    const item = queue.shift()
    
    if (item.right) {
      queue.unshift(item.right)
    }
    if (item.left) {
      queue.unshift(item.left)
    }
    callback(item.value)
  }
}