fix(cdk/tree): retainining previous objects

fixes component retaining old data in memory even when its not used causing memory usage to increase

fixes #30322

Author: naaajii

src/cdk/tree/tree.ts

@@ -1066,6 +1066,9 @@ export class CdkTree<T, K = T>
     // nodes are flat, or if the tree is using a levelAccessor and the nodes are
     // nested.
     if (this.childrenAccessor && nodeType === 'flat') {
+      // clear previously generated data so we don't keep end up retaining data overtime causing
+      // memory leaks.
+      this._clearPreviousCache();
       // This flattens children into a single array.
       this._ariaSets.set(null, [...nodes]);
       return this._flattenNestedNodesWithExpansion(nodes).pipe(
@@ -1098,6 +1101,9 @@ export class CdkTree<T, K = T>
         }),
       );
     } else {
+      // clear previously generated data so we don't keep end up retaining data overtime causing
+      // memory leaks.
+      this._clearPreviousCache();
       // For nested nodes, we still need to perform the node flattening in order
       // to maintain our caches for various tree operations.
       this._ariaSets.set(null, [...nodes]);
@@ -1125,8 +1131,9 @@ export class CdkTree<T, K = T>
       return;
     }
 
-    this._parents.clear();
-    this._ariaSets.clear();
+    // clear previously generated data so we don't keep end up retaining data overtime causing
+    // memory leaks.
+    this._clearPreviousCache();
 
     for (let index = 0; index < flattenedNodes.length; index++) {
       const dataNode = flattenedNodes[index];
@@ -1163,6 +1170,13 @@ export class CdkTree<T, K = T>
       callback(toToggle);
     }
   }
+
+  /** Clears the maps we use to store parents, level & aria-sets in. */
+  private _clearPreviousCache() {
+    this._parents.clear();
+    this._levels.clear();
+    this._ariaSets.clear();
+  }
 }
 
 /**