Transact SQL :: Table With SPARSE Column Need More Space?

As I understood, if SPARSE is used on a column, which have many NULL marks, then the storage could be efficently used (we need less spaces to save NULL marks, hence a table which has many NULL marks with SPARSE property needs less storage than the same table, but without SPARSE. I created two table as follow:

/******* Table with Sparse ******/CREATE TABLE Sprstb(
unsprsid INT IDENTITY(1,1) NOT NULL,
Firstname varchar(20) NOT NULL,
Lastname varchar(20) NOT NULL,
Tel int NOT NULL,
adress nvarchar(60) SPARSE NULL)/***** Table without Sparse*******/CREATE TABLE Unsprstb(unsprsid INT IDENTITY(1,1) NOT NULL,Firstname varchar(20) NOT NULL,
Lastname varchar(20) NOT NULL,
Tel int NOT NULL,
address nvarchar(60) NULL)

I have populated the Sprstb with 5 Milion records. It needs 509,961 MB storage. Then I have copied this table into Unsprstb

SET IDENTITY_INSERT [dbo].[Unsprstb] ON
Insert [dbo].[Unsprstb](unsprsid,Firstname,Lastname,Tel,adress)
SELECT unsprsid,Firstname,Lastname,Tel, adress FROM [dbo].[Sprstb]
SET IDENTITY_INSERT [dbo].[Unsprstb] OFF
The Unssprstb need only  466,031MB !

That means the Table with SPARSE column need more storage, Why? 

By the way, in table Sprstb column address has  1666198  Null mark (from 5000000)