chore(tree): revert treenode.children to querylist, add comment

Author: ViktorSlavov

projects/igniteui-angular/src/lib/tree/tree-node/tree-node.component.ts

@@ -88,9 +88,11 @@ export class IgxTreeNodeComponent<T> extends ToggleAnimationPlayer implements Ig
     @HostBinding('class.igx-tree-node')
     public cssClass = 'igx-tree-node';
 
+    // TODO: Public API should expose array or null, not query list
     @ContentChildren(IGX_TREE_NODE_COMPONENT, { read: IGX_TREE_NODE_COMPONENT })
-    private _children: QueryList<IgxTreeNode<any>>;
+    public children: QueryList<IgxTreeNode<any>>;
 
+    // TODO: Refactor `children` to get `this.children.toArray() || null`
     /**
      * Return the child nodes of the node (if any)
      *
@@ -102,8 +104,8 @@ export class IgxTreeNodeComponent<T> extends ToggleAnimationPlayer implements Ig
      * const children: IgxTreeNode<any>[] = node.children;
      * ```
      */
-    public get children(): IgxTreeNode<any>[] {
-        return this._children?.length ? this._children.toArray() : null;
+    public get _children(): IgxTreeNode<any>[] {
+        return this.children?.length ? this.children.toArray() : null;
     }
 
     @ViewChild('defaultSelect', { read: TemplateRef, static: true })

projects/igniteui-angular/src/lib/tree/tree-selection.service.ts

@@ -251,7 +251,7 @@ export class IgxTreeSelectionService {
      * Handle the selection state of a given node based the selection states of its direct children
      */
     private handleNodeSelectionState(node: IgxTreeNode<any>) {
-        const nodesArray = (node && node.children) ? node.children : [];
+        const nodesArray = (node && node.children) ? node.children.toArray() : [];
         if (nodesArray.length) {
             if (nodesArray.every(n => this.nodesToBeSelected.has(n))) {
                 this.nodesToBeSelected.add(node);