Logstash Service doesn't load .conf file

Dear all,
I have problem with my Logstash (I don't know it is really problem or not).

I have installed Logstash on my UbuntuServer with recommended manner described on Logstash official page (I use apt-get install to install Logstash). Now, when I use logstash -f PATH-TO-CONF-FILE, it works based on the my desired config file; but when I use "sudo service logstash start", it doesn't work based on the conf file in /etc/logstash/logstash.conf/MY_CONF_FILE.

how can I set up my logstash to start with my desired config file. Is it possible ?

Thanks in advance.

it doesn't work based on the conf file in /etc/logstash/logstash.conf/MY_CONF_FILE.

Logstash expects configuration files to be stored in /etc/logstash/conf.d.