$ sudo apt-get install php

$ php -v
PHP 7.0.8-0ubuntu0.16.04.3 (cli) ( NTS )

$ php -r "echo 'Hello World!'.PHP_EOL;"
Hello World!

$ sudo apt-get install apache2

$ curl http://localhost

<?php

define("ASTER", "* ");
define("SPACE", " ");
define("EVE", 24);

$sumAster = 0;
$step = 0;

while($sumAster <= EVE) {
    $step ++;
    $sumAster += $step;
}
$trnk = EVE - ($sumAster - $step);

for ($i = 1; $i <= $step; $i++){
    if ($i < $step) {
        for ($j = $step; $j > $i; $j--) echo SPACE;
        for ($j = 1; $j <= $i; $j++)    echo ASTER;
    } else {
        for ($j = $i - $trnk; $j >= 1; $j--) echo SPACE;
        for ($j = 1; $j <= $trnk; $j++)      echo ASTER;
    }
    echo PHP_EOL;
}

$ php tree.php 
      * 
     * * 
    * * * 
   * * * * 
  * * * * * 
 * * * * * * 
    * * *