How to write a script to automatically build a ref tree?

Question

JavaScript

Guys, the next question. We need a script that, based on this database, would build a tree. The task is interesting, and something tells me that it is elementary. This is what brought me into a stupor:
parent is the one who is OVER the person. The one who is UNDER is not registered in the database. And I'm a little confused.
Please help me on the best way to accomplish this task.
Here is a screenshot of the table

Answer 1

You define a variable r1 and then use p instead. The else if conditions are written backwards. When cast to a number, the same variable is written differently.

function f1(){
  var nu1, nu2, r1;
  nu1 = document.getElementById('n1').value;
  nu1 = parseInt(nu1);

  nu2 = document.getElementById('n2').value;
  nu2 = parseInt(nu2);

  r1 = document.getElementById('r');

  if (nu1>nu2){
    r1.innerHTML = 'Первое число больше второго!';
  }
  else if(nu1==nu2){
    r1.innerHTML = 'Числа равны!!';
  }
    else{
    r1.innerHTML = 'Второе число больше первого!';
  }
}

Answer 2

Google nested sets
There are a lot of materials on the net.
And normal forms are violated in the database - you have several columns parent, parent2, ...
In this case, they must be moved to a separate table, otherwise problems will arise in the future.