Adding children to PrimeNg TreeTable programmatically

I'd like to add childNodes to a TreeTable programmatically. There's no problem adding the parent-nodes like:

var parentNode: TreeNode = { data: {
        'col1': 'aaa',
        'col2': 'aaa',
      }};

this.treeTableModel.push(parentNode);

But when I'm trying to do:

parentNode.children.push(childNode);

Children is undefined?

What's the best way to implement this?

first, you can look at TreeNode api here: https://github.com/primefaces/primeng/blob/bb1792eac98c7beb9d18ff68bed99408ad650108/components/common/api.ts

second, you initialized parentNode like this

var parentNode: TreeNode = { data: {
        'col1': 'aaa',
        'col2': 'aaa',
      }};

parentNode has no property children at this point. You'll have to add it. children is a TreeNode array: TreeNode[] so what you can do is:

var parentNode: TreeNode =
       { 
        data: {
          'col1': 'aaa',
          'col2': 'aaa',
         },
         children:[];
       };

now that children is initialized as an empty array, you can push to it:

this.treeTableModel.push(parentNode);