Selecting parent node does not select child node with hasChildren true in angular-tree-component

Question

I am using angular-tree-component v7.2.0 with angular 5.

HTML

<tree-root #treeRoot [nodes]="nodesOfSites" [options]="options"></tree-root>

TS

nodesOfSites = []; 
options: any = { useCheckbox: true, getChildren: (node: TreeNode) => this.getChildren(node) };

When I select the parent node, it does not select all child nodes. All the child nodes with hasChildren: false get selected but child nodes with hasChildren: true does not get selected.