insert all 
 into table_a(column_a,column_b,column_c) values(value_1a,value_1b,value_1c)
 into table_a(column_a,column_b,column_c) values(value_2a,value_2b,value_2c)
 select * from dual 

もしくは、カラム指定を省略して

insert all 
 into table_a values(value_1a,value_1b,value_1c)
 into table_a values(value_2a,value_2b,value_2c)
 select * from dual