laravel getting all child parents relation ship

Question

in our application which that used laravel we implemented parent-child structure with data base relation ship. for example:

all ids are sample in this structure:

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each parent in our database started and pointed with null and each child has parent id. now when we try to get all parents of laravel we should have:

backend - web programmings - programmings 

Category model structure:

/**
 * Get the parent Category to which the current Category belongs.
 */
public function parent(): BelongsTo
{
    return $this->belongsTo(Category::class, 'parent_id', 'id', 'parent');
}

/**
 * Get all Categories which belong to the current Category.
 */
public function subcategories(): HasMany
{
    return $this->hasMany(Category::class, 'parent_id', 'id');
}

i getting one level of child parent but i don't know how can i get all parents of child til arrived to null

getting all posts based on role:

controller:

$categories = auth()->user()->availableCategories();

HasPosts trait:

trait HasCategories
{
    public function availableCategories(): Collection
    {
        $categories = $this->categories;

        $parents = $categories->filter(function ($cat) use ($categories) {
            return !in_array($cat->parent_id, $categories->pluck('id')->all()) || is_null($cat->parent_id);
        });

        $parents->map(
            fn ($parent) => $this->setNested($parent, $categories)
        );

        return $parents;
    }

    /**
     * Get all Categories with Posts associated with the User in nested tree structure.
     */
    public function availableCategoriesWithPosts(): Collection
    {
        $categories = $this->categories()->withPosts()->get();

        $parents = $categories->filter(
            fn ($cat) =>
            !$categories->contains('id', $cat->parent_id) || is_null($cat->parent_id)
        );

        $parents->map(fn ($parent) => $this->setNested($parent, $categories));

        return $parents;
    }
        
           
    protected function setNested($parent, $categories)
    {
        $parent->setRelation('subcategories', $categories->where('parent_id', $parent->id));
        $parent->subcategories->map(function ($sub) use ($categories) {
            if ($categories->contains('parent_id', $sub->id)) {
                $this->setNested($sub, $categories);
                return $sub;
            }
        });
    }
}

i try this code:

public function parent(): BelongsTo
{
    return $this->belongsTo(Category::class, 'parent_id', 'id', 'parent')->with('parent');
}