Use a group by to have as results a count of 'value = x' and a count of 'value

I'm writing a query in Oracle SQL. I'm using a count - group by query, for example:

select column_a, count(*)
from table_1
group by column_a

COLUMN_A    COUNT(*)

value_1     5
value_2     6
value_3     2
(null)      1

Can I write a group by that allows me to get two result rows, one with value_1 and its count, and another with the count of all other values? It would look like this:

COLUMN_A    COUNT(*)

value_1     5
others      9