fix(query-builder): bug where new conditions don't have parent

Author: ivanvpetrov

projects/igniteui-angular/src/lib/query-builder/query-builder-tree.component.ts

@@ -802,6 +802,7 @@ export class IgxQueryBuilderTreeComponent implements AfterViewInit, OnDestroy {
             this._lastFocusedChipIndex++;
         } else {
             this.rootGroup = groupItem;
+            operandItem.parent = groupItem;
             this.rootGroup.children.push(operandItem);
             this._lastFocusedChipIndex = 0;
         }

src/app/query-builder/query-builder.sample.ts

@@ -253,6 +253,8 @@ export class QueryBuilderComponent implements OnInit {
                 conditionName: IgxStringFilteringOperand.instance().condition('notNull').name
             });
             tree.filteringOperands.push(subGroup2);
+            
+            this.expressionTree = tree;
         }
         this.lData = [{ id: 0, field: 'a' }, { id: 1, field: '1' }]
         // this.onChange();