Add call button not present when in active call

Hi all,

I have a MacBook Pro (the latest one with Yosemite 10.10.2). I dont have an iPhone so no integration has been done. I was watching Modern Family - "Connection Lost" episode and I saw Claire adding another call when she was in a Facetime video call.

But I dont have a green color "Add Call" button on the top right in my device. I searched online and found info similar to what she did like "End current call and answer" or "Accept call" options when another call comes in. But I cant find these in mine.

Can someone help me out with this?