How to save One to Many Relationship to database

Below is my LevelOneModel. I can't seem to figure out what I have not included. Please I need assistance.

What I want to achieve is to have all the users id in the levelone table

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;


class LevelOneModel extends Model
{
public function users(){
    return $this->hasMany('App\User');
}

}

Below is my User model

<?php

namespace App;

use Illuminate\Notifications\Notifiable;
use Illuminate\Foundation\Auth\User as Authenticatable;


class User extends Authenticatable
{
use Notifiable;

/**
 * The attributes that are mass assignable.
 *
 * @var array
 */
protected $fillable = [
    'first_name', 
    'last_name', 
    'email',
    'phone',
    'bank_name',
    'acct_name',
    'acct_number',
    'profile_pix',
    'sme',
    'other_sme',
    'password',
];

public function levelone()
{
    return $this->belongsTo('App\LevelOneModel');
}

/**
 * The attributes that should be hidden for arrays.
 *
 * @var array
 */
protected $hidden = [
    'password', 'remember_token',
];
}

And below is my level one migration file

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateLevelOneTable extends Migration
{
/**
 * Run the migrations.
 *
 * @return void
 */
public function up()
{
    Schema::create('level_one', function (Blueprint $table) {
        $table->increments('id');
        $table->integer('users_id')->unsigned();
        $table->integer('upline_id')->nullable();
        $table->timestamps();
    });
}

/**
 * Reverse the migrations.
 *
 * @return void
 */
public function down()
{
    Schema::dropIfExists('level_one');
}
}

Thanks

via Chebli Mohamed