I heard that Streams is part of Oracle Enterprise edition.wrong
Is there any way we can implement bi-directional and uni-directional replication by using Oracle Standard Edition?yes
wrongThe documentation at http://docs.oracle.com/cd/E11882_01/license.112/e10594/editions.htm#CJACGHEB clearly mentions that multi - master replication is only part of Enterprise edition only. Check under Integration section.
Low cost - Multidirectional Streams replication has less configuration costs than RAC and it's free with Oracle Enterprise Edition.whereas the documentation at http://docs.oracle.com/cd/E11882_01/license.112/e10594/editions.htm#CJACGHEB says that oracle stream is available in standard edition as well.