Knockout If-else condition inside html file in Magento 2

You should write a below code for else condition

<!-- ko if: isFreeShipping() -->
    //My Code goes here
<!-- /ko -->
<!-- ko ifnot: isFreeShipping() -->
    //My Code goes here
<!-- /ko -->

Just to extend a bit on Suresh Chikani's answer to include more combinations under this question:

To do a if-elseif-else construction you would have in PHP:

if (A && B) {
    //...code
} elseif (A) { // And thus 'not B'
    //...code
} else { // Thus is 'not A' and 'not B'
    //...code
}

In Knockout you would do:

<!-- ko if: A && B -->
    //...code
<!-- /ko -->
<!-- ko if: A && !B -->
    //...code
<!-- /ko -->
<!-- ko if: !A && !B -->
    //...code
<!-- /ko -->