Can PHP convert a 2D array w/ 3 cols to a hierarchical structure w/o assoc. keys?

I have data like this:

Which can also be seen as this PHP array:

$items = [
    ['item1' => 'a', 'item2' => 'c', 'item3' => 'h'],
    ['item1' => 'a', 'item2' => 'c', 'item3' => 'i'],
    ['item1' => 'a', 'item2' => 'd', 'item3' => 'j'],
    ['item1' => 'a', 'item2' => 'd', 'item3' => 'k'],
    ['item1' => 'b', 'item2' => 'e', 'item3' => 'l'],
    ['item1' => 'b', 'item2' => 'e', 'item3' => 'm'],
    ['item1' => 'b', 'item2' => 'f', 'item3' => 'n'],
    ['item1' => 'b', 'item2' => 'g', 'item3' => 'o'],
];

Or even this (multidimensional) list:

a
    c
        h
        i
    d
        j
        k
b
    e
        l
        m
    f
        n
    g
        o

How could I loop through this data and create a multidimensional array like

$items = [
    [a, [[c, [h, i]], [d, [j, k]]],  
    [b, [[e, [l, m]], [f, [n]], [g, [o]]]
];

Basically my aim to build the multidimensional html list, but my brain is stuck.
With the multidimensional array I’d be able to do it.

Thanks!

Here’s an attempt to solve it.
It’s a bit more complicated example.
And it’s "too hard coded".
There are some errors in the indexes.

I’m wondering if there’s a cleaner approach.

<?php

$items = [
    ['item1' => 'a', 'item2' => 'c', 'item3' => 'd2', 'item4' => 'f'],
    ['item1' => 'a', 'item2' => 'c', 'item3' => 'd2', 'item4' => 'g'],
    ['item1' => 'a', 'item2' => 'd', 'item3' => 'd3', 'item4' => 'h'],
    ['item1' => 'a', 'item2' => 'd', 'item3' => 'e', 'item4' => 'i'],
    ['item1' => 'b', 'item2' => 'c', 'item3' => 'e', 'item4' => 'j'],
    ['item1' => 'b', 'item2' => 'c', 'item3' => 'e', 'item4' => 'k'],
    ['item1' => 'b', 'item2' => 'c', 'item3' => 'e', 'item4' => 'l'],
    ['item1' => 'b', 'item2' => 'c2', 'item3' => 'e', 'item4' => 'm'],
];


        $items_new = [];

        $item1 = '';
        $item2 = '';
        $item3 = '';
        $item4 = '';

        foreach ($items as $item):

          $item1_new = $item['item1'];
          $item2_new = $item['item2'];
          $item3_new = $item['item3'];
          $item4_new = $item['item4'];

          if($item1 != $item1_new)
          {
            $items_new[] = [$item1_new, []];

            $item1 = $item1_new;

            $item2 = '';
          }
          
          if($item2 != $item2_new)
          {
            $items_new[count($items_new) - 1][] = [$item2_new, []];

            $item2 = $item2_new;

            $item3 = '';
          }

          if($item3 != $item3_new)
          {
            $items_new[count($items_new) - 1][count($items_new[1]) - 1][] = [$item3_new, []];

            $item3 = $item3_new;

            $item4 = '';
          }

          if($item4 != $item4_new)
          {
            $items_new[count($items_new) - 1][count($items_new[1]) - 1][count($items_new[2]) - 1][] = [$item4_new, []];

            $item4 = $item4_new;
          }


        endforeach;
 


        foreach($items_new as $items1)
        {
          if (is_string($items1))
          {
            echo $items1 . '<br>';
          }
          elseif (is_array($items1))
          {
            foreach($items1 as $items2)
            {
                if (is_string($items2))
                {
                  echo  ' - ' . $items2 . '<br>';
                }
                elseif (is_array($items2))
                {
                  foreach ($items2 as $items3)
                  {
                    if (is_string($items3))
                    {
                      echo  ' --- ' . $items3 . '<br>';
                    }
                    elseif (is_array($items3))
                    {
                      foreach ($items3 as $items4)
                      {
                        if (is_string($items4))
                        {
                          echo  ' ----- ' . $items4 . '<br>';
                        }
                        elseif (is_array($items4))
                        {
                          foreach ($items4 as $items5)
                          {
                            if (is_string($items5))
                            {
                              echo  ' ------- ' . $items5 . '<br>';
                            }
                            elseif (is_array($items5))
                            {
                              foreach ($items5 as $items6)
                              {
                                
                              }
                            }
                          }
                        }
                      }
                    }
                  }
                }
            }
          }
        }
        ?>