how to generate ordered sequence for n number of n number of child

PFB code

 create table tab1 (id int, rivername varchar(100), parentid int)

insert into tab1 (id, rivername, parentid)
values (1,'r1',null),
(3,'r2',null),
(2,'r3',null),
(4,'akash',3),
(5,'xyz',3),
(6,'r5',null),
(7,'abc',3),
(8,'hkjd',4),
(10,'ksjdf',7),
(19,'ksjdf',7),
(14,'jjj',null)


Alter Function udt_getHirarcy(@Iid Varchar(100))
Returns  Varchar(100)
AS
Begin
Declare @Return varchar(100)=@Iid ,@Gid varchar(30) =@Iid ,@tempParentid varchar(20)
while(1=1)
Begin
        select @Return = case when parentid is null then @Iid+ '.0'
        else    convert(varchar,parentid) +  replicate ('0', 3 - len(convert(varchar,parentid))) end + @Return 
        ,@tempParentid=parentid from tab1 where id = @Iid
        if @@ROWCOUNT < 1 or @tempParentid is null
        Break
        select @Iid = @tempParentid
END
Return @Return  
END
GO

select convert(float,dbo.udt_getHirarcy(id)) hie,* from tab1
order by hie

Thanks

Saravana Kumar C