How to add child node in parent.

Hi, anybody please tell me how to add children data in parent node,

handleClickOnItem(rowInfo) {
const NEW_NODE = [ { title: 'A }, { title: 'B }, { title: 'C }, { title: 'D }];
const newTree = addNodeUnderParent({
treeData: this.state.treeData,
newNode: NEW_NODE,
expandParent: true,
parentKey: rowInfo ? rowInfo.treeIndex : undefined,
getNodeKey: ({ treeIndex }) => treeIndex,
});
this.setState({ treeData: newTree.treeData })
}

i am trying to add children array inside the parent, but its not working,