SQL Server 2012 :: Error When Passing Multiple Rows

I am getting error when I passed multiple rows in less than condition:

create table #t1
( ID int)
INSERT INTO #t1

SELECT 1 UNION ALL SELECT 5 UNION ALL SELECT 8
CREATE TABLE #t2
(ID int)
INSERT INTO #t2
SELECT 3 UNION ALL SELECT 20 UNION ALL SELECT 4

SELECT ID FROM #t2
WHERE ID < (SELECT ID FROM #t1)

Error is: Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

How to pass multiple values in this condition?