bst = Object.create({
  empty() {
    this.value = null
    this.left = null
    this.right = null
  },

  show() {
    let output = `${this.value}`
    
    if (this.left && this.right) {
      output = `  ${output}\n / \\\n${this.left.value}  ${this.right.value}`
    } else if (this.left) {
      output = `  ${output}\n /\n${this.left.value}`
    } else if (this.right) {
      output = `${output}\n  \\\n   ${this.right.value}`
    }
  
    console.log(output)
  
    if (this.left?.left?.value || this.left?.right?.value) this.left.show()
    if (this.right?.left?.value || this.right?.right?.value) this.right.show()
  },

  add(value) {
    if (this.value === undefined || this.value === null) {
      this.value = value
    } else {
      if (value < this.value) {
        if (!this.left || this.left.value === undefined || this.left === null) {
          this.left = Object.assign(Object.create(Object.getPrototypeOf(this)), {value})
        } else {
          this.add.call(this.left, value)
        }
      } else if (value > this.value) {
        if (!this.right || this.right.value === undefined || this.right === null) {
          this.right = Object.assign(Object.create(Object.getPrototypeOf(this)), {value})
        } else {
          this.add.call(this.right, value)
        }
      }
    }
    this.show()
  },
})