diff --git a/packages/core/src/menu/MenuLevelBuilder.tsx b/packages/core/src/menu/MenuLevelBuilder.ts
similarity index 71%
rename from packages/core/src/menu/MenuLevelBuilder.tsx
rename to packages/core/src/menu/MenuLevelBuilder.ts
index 81ab9899c..01da8ab0f 100644
--- a/packages/core/src/menu/MenuLevelBuilder.tsx
+++ b/packages/core/src/menu/MenuLevelBuilder.ts
@@ -10,7 +10,7 @@ export type MenuTree<Item extends BaseMenuItem> = Item & {
 }
 
 export class MenuLevel<Item extends BaseMenuItem> {
-  constructor(public items: Item[] = [], public activeId: string = '') {}
+  constructor(public items: Item[], public activeId: string) {}
 }
 
 export class MenuLevelBuilder<Item extends BaseMenuItem> {
@@ -19,12 +19,11 @@ export class MenuLevelBuilder<Item extends BaseMenuItem> {
   protected buildLevels(
     activeId: string,
     items: MenuTree<Item>[],
-    levels: MenuLevel<Item>[],
+    levels: (MenuLevel<Item> | undefined)[],
     depth = 0,
     parentActive = false
   ): boolean {
-    if (levels.length <= depth) levels[depth] = new MenuLevel()
-    const level = levels[depth]
+    if (levels.length <= depth) levels.push(undefined)
     let activeItem: MenuTree<Item> | undefined
     for (let item of items) {
       const currentActive = item.id === activeId
@@ -43,12 +42,11 @@ export class MenuLevelBuilder<Item extends BaseMenuItem> {
       if (childActive && !activeItem) activeItem = item
     }
 
-    if (activeItem) {
-      level.items = items
-      level.activeId = activeItem.id
-    } else if (parentActive) {
-      level.items = items
-      level.activeId = items[0].id
+    if (activeItem || parentActive) {
+      levels[depth] = new MenuLevel(
+        items,
+        activeItem ? activeItem.id : items[0].id
+      )
     }
 
     return !!activeItem
@@ -56,11 +54,12 @@ export class MenuLevelBuilder<Item extends BaseMenuItem> {
 
   /**
    * Split MenuTree structure to levels.
+   * Returns array, where index is a menu level.
    *
    * @param activeId current menu item id
    */
-  levels(activeId: string): MenuLevel<Item>[] {
-    const result: MenuLevel<Item>[] = []
+  levels(activeId: string): (MenuLevel<Item> | undefined)[] {
+    const result: (MenuLevel<Item>[] | undefined) = []
     this.buildLevels(activeId, this.items, result)
     return result
   }