Using same disposable object twice in diffrent using-statment

Question

I have made a disposable class UnitOfWOrk which will also acts as an optional parameter, I have provided an exampel below.

public async Task CallPersistItemPassUoW()
{
    using (var unitOfWork = new UnitOfWork(_connectionString, openTransaction: true))
    {
        try
        {
            await PersistItem(25, unitOfWork);
            unitOfWork.Transaction.Commit();
        }
        catch (Exception)
        {
            unitOfWork.Transaction.Rollback();
        }
    }
}

public async Task CallPersistItem()
{
    await PersistItem(30);
}

public static async Task PersistItem(int itemId, UnitOfWork ouw = null)
{
    using (var unitOfWork = ouw ?? new UnitOfWork(_connectionString))
    {
        await unitOfWork.Connection.ExecuteScalarAsync(
            "insert into [dbo].[ItemTable](ItemId) values(@ItemId)",
            new
            {
                ItemId = itemId
            },
            unitOfWork.Transaction);
    }
}

As you can see both the methods CallPersistItemPassUoW and CallPersistItem calls the method PersistItem. CallPersistItemPassUoW passes a used UnitOfWork while CallPersisItem doesn't pass anything. If the parameter ouw (in the method PersistItem) doesn't have a value a new instance of UnitofWork is used in the using-statment otherwise the parameter is used in the using-stamtent. This means that the same UnitOfWork instance could be used twice, is that a problem in this case? If CallPersistItemPassUoW would call PersistItem would the instance of UnitOfWork be dispoced in CallPersistItemPassUoW or in PersistItem?

Thank you!