Filament excel export multiple sheets from relations

Question

I'm using this filament-excel package to export my table data.

I tried to export all data from my table with their relationship

So , I'm expecting the results to be 2 excel sheets the main sheet will be the parent model, and another sheet will be the child model

Lets say i have two model here, Invoice and InvoiceItem

class Invoice extends Model
{
    use HasFactory;

    public function items(): HasMany
    {
        return $this->hasMany(InvoiceItem::class);
    }
}

class InvoiceItem extends Model
{
    use HasFactory;

    public function invoice(): BelongsTo
    {
        return $this->belongsTo(Invoice::class);
    }
}

I have follow the documentation, by using the bulk export like so:

public static function table(Table $table): Table
{
    return $table
        ->bulkActions([
            ExportBulkAction::make()
        ])
} 

But i haven't got the clue how to add the relationship to the export class How can i solve this ?