package main

import "fmt"

type tree []node

type node struct {
    label    string
    children []int // indexes into tree
}

func main() {
    vis(tree{
        0: node{"root", []int{1, 2, 3}},
        1: node{"ei", []int{4, 5}},
        2: node{"bee", nil},
        3: node{"si", nil},
        4: node{"dee", nil},
        5: node{"y", []int{6}},
        6: node{"eff", nil},
    })
}

func vis(t tree) {
    if len(t) == 0 {
        fmt.Println("<empty>")
        return
    }
    var f func(int, string)
    f = func(n int, pre string) {
        ch := t[n].children
        if len(ch) == 0 {
            fmt.Println("╴", t[n].label)
            return
        }
        fmt.Println("┐", t[n].label)
        last := len(ch) - 1
        for _, ch := range ch[:last] {
            fmt.Print(pre, "├─")
            f(ch, pre+"│ ")
        }
        fmt.Print(pre, "└─")
        f(ch[last], pre+"  ")
    }
    f(0, "")
}