Custom .png file instead of ‘ionic icon’ in <ion-tab> in ionic2

I am facing one issue. Can you help me in it please? I am stuck in that issue from last 3 days.
how can I put custom .png file instead of default ionic icon?

check my code below:
<ion-tab [root]=“tab2Root” tabTitle=“Categories” tabIcon=“home”>

Here I have put ionic’s icon in “tabIcon” attribute.
But what should I do if I want to add my custom .png file there in IONIC2.