Model Relationships not yielding desried result

So guys, i need some help. First of all, i would like to thoroughly understand defining relationships using eloquent. My situation is that i have a category model that is n-level deep. I also have services that belongs to a category irrespective of its depth.

Below is my category model

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Category extends Model
{
    use HasFactory;

    /**
     * The attributes that are mass assignable.
     *
     * @var string[]
     */
    protected $fillable = [
        'title',
        'subtitle',
        'category_id',
        'img',
        'video',
        'status',
    ];

    public function parent()
    {
        return $this->belongsTo(Category::class, 'category_id');
    }

    public function children()
    {
        return $this->hasMany(Category::class, 'category_id');
    }

    public function addons()
    {
        return $this->hasMany(AddOn::class);
    }

    public function timeslots()
    {
        return $this->hasMany(TimeSlot::class);
    }

    public function banners() {
        return $this->hasMany(Banner::class);
    }

    public function partnerservices() {
        return $this->hasMany(PartnerService);
    }
}

And Here is my PartnerService Model

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class PartnerService extends Model
{
    use HasFactory;

    protected $fillable = [
        'image',
        'video',
        'title',
        'discount',
        'time_taken',
        'max_quantity',
        'price',
        'status',
        'which_to_show',
        'category_id',
        'sub_category_id',
        'child_category_id',
        'service_description'
    ];

    public function category() {
        return $this->belongsTo(Category::class, 'category_id');
    }

    public function booking() {
        return $this->hasMany(Booking::class);
    }

    public function ratings()
    {
        return $this->hasMany(Rating::class);
    }
}

Now when i query the relationship from a first level category i.e a category that has no parent then i can get the partner services using the "with['partnerservices']" in my controller. However when i try to do the same with a category that has a parent, this returns as empty, even when the service belongs to a category.