PL/SQL :: Unable To Create Logic Sequence?

create table t (a varchar2(20),b number(8));
insert into t values ('aa',4);
insert into t values ('ba',6);
insert into t values ('ca',7);
insert into t values ('da',8);

in place of 8 there can be any number between 1 to 100

if in place of 8 number is <10
insert into t values('ea',10); ---- this i need dynamic insert
if in place of the number between 11-19 then
insert into t values('ea',20); ---- this i need dynamic insert
and so on

i tried as below

select case when max(b) <10 then 10 when max(b) between 10 and 20 then 20 end from t;

but i cant write case for again and again upto nth