diff --git a/uno-core/src/main/java/cc/allio/uno/core/api/Single.java b/uno-core/src/main/java/cc/allio/uno/core/api/Single.java
new file mode 100644
index 00000000..1241aaf0
--- /dev/null
+++ b/uno-core/src/main/java/cc/allio/uno/core/api/Single.java
@@ -0,0 +1,131 @@
+package cc.allio.uno.core.api;
+
+import cc.allio.uno.core.exception.Exceptions;
+import cc.allio.uno.core.util.CollectionUtils;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.stream.Stream;
+
+/**
+ * description 'single' value transfer and filter.
+ *
+ * @author j.x
+ * @date 2024/7/6 17:57
+ * @since 0.1.1
+ * @see Stream
+ */
+public interface Single<E> {
+
+    /**
+     * from {@link List} single
+     *
+     * @param list the list
+     * @return the {@link Single} instance
+     */
+    static <E> Single<E> from(List<E> list) {
+        if (CollectionUtils.isEmpty(list)) {
+            throw Exceptions.unNull("list");
+        }
+        return new InternalSingle<>(list.stream());
+    }
+
+    /**
+     * from {@link Set} single
+     *
+     * @param set the set
+     * @return the {@link Single} instance
+     */
+    static <E> Single<E> from(Set<E> set) {
+        if (CollectionUtils.isEmpty(set)) {
+            throw Exceptions.unNull("set");
+        }
+        return new InternalSingle<>(set.stream());
+    }
+
+    /**
+     * from {@link Map} single
+     *
+     * @param map the map
+     * @return the {@link Single} instance
+     */
+    static <E, K, V> Single<E> from(Map<K, V> map) {
+        if (CollectionUtils.isEmpty(map)) {
+            throw Exceptions.unNull("map");
+        }
+        return (Single<E>) new InternalSingle<>(map.entrySet().stream());
+    }
+
+    /**
+     * from {@link Stream} single
+     *
+     * @param stream the stream
+     * @return the {@link Single} instance
+     */
+    static <E> Single<E> from(Stream<E> stream) {
+        if (stream == null) {
+            throw Exceptions.unNull("map");
+        }
+        return new InternalSingle<>(stream);
+    }
+
+    /**
+     * single elements trigger map operator
+     *
+     * @param func the map function
+     * @return the {@link Single} instance
+     */
+    <V> Single<V> map(Function<E, V> func);
+
+    /**
+     * single elements trigger filter operator
+     *
+     * @param predicate the predicate function
+     * @return the {@link Single} instance
+     */
+    Single<E> filter(Predicate<E> predicate);
+
+    /**
+     * foreach all elements, if one of through predicate, then return element of {@link Optional} instance, otherwise
+     * return empty
+     *
+     * @param predicate the element predicate
+     * @return the {@link Optional} instance
+     */
+    Optional<E> forReturn(Predicate<E> predicate);
+
+    class InternalSingle<E> implements Single<E>, Self<InternalSingle<E>> {
+
+        private Stream<E> stream;
+
+        public InternalSingle(Stream<E> stream) {
+            this.stream = stream;
+        }
+
+        @Override
+        public <V> Single<V> map(Function<E, V> func) {
+            return new InternalSingle<>(stream.map(func));
+        }
+
+        @Override
+        public Single<E> filter(Predicate<E> predicate) {
+            this.stream = stream.filter(predicate);
+            return self();
+        }
+
+        @Override
+        public Optional<E> forReturn(Predicate<E> predicate) {
+            List<E> elements = stream.toList();
+            for (E element : elements) {
+                if (predicate.test(element)) {
+                    return Optional.ofNullable(element);
+                }
+            }
+            return Optional.empty();
+        }
+    }
+}
diff --git a/uno-core/src/main/java/cc/allio/uno/core/concurrent/MultiCheckedException.java b/uno-core/src/main/java/cc/allio/uno/core/concurrent/MultiCheckedException.java
index e45304dc..64d52948 100644
--- a/uno-core/src/main/java/cc/allio/uno/core/concurrent/MultiCheckedException.java
+++ b/uno-core/src/main/java/cc/allio/uno/core/concurrent/MultiCheckedException.java
@@ -1,5 +1,6 @@
 package cc.allio.uno.core.concurrent;
 
+import cc.allio.uno.core.api.Single;
 import com.google.common.collect.Maps;
 
 import java.util.Map;
@@ -14,8 +15,8 @@
 public class MultiCheckedException extends Exception {
 
     // 受检查的异常
-    final Map<Class<? extends Throwable>, Throwable> checked = Maps.newHashMap();
-    final Map<Class<? extends RuntimeException>, RuntimeException> unchecked = Maps.newHashMap();
+    final transient Map<Class<? extends Throwable>, Throwable> checked = Maps.newHashMap();
+    final transient Map<Class<? extends RuntimeException>, RuntimeException> unchecked = Maps.newHashMap();
 
     /**
      * 追加异常
@@ -39,11 +40,14 @@ public <T extends Throwable> void appendException(T ex) {
      * @return Exception or null
      */
     public <T extends RuntimeException> T findUncheckedException(Class<T> errType) {
-        RuntimeException err = unchecked.get(errType);
-        if (err != null) {
-            return (T) err;
+        if (hasUncheckedException(errType)) {
+            return (T) unchecked.get(errType);
         }
-        return null;
+        var err = Single.from(unchecked.entrySet())
+                .forReturn(errEntry -> errEntry.getKey().isAssignableFrom(errType))
+                .map(Map.Entry::getValue)
+                .orElse(null);
+        return (T) err;
     }
 
     /**
@@ -54,11 +58,15 @@ public <T extends RuntimeException> T findUncheckedException(Class<T> errType) {
      * @return Exception or null
      */
     public <T extends Throwable> T findCheckedException(Class<T> errType) {
-        Throwable err = checked.get(errType);
-        if (err != null) {
-            return (T) err;
+        if (hasCheckedException(errType)) {
+            return (T) checked.get(errType);
         }
-        return null;
+        var err = Single.from(checked.entrySet())
+                .forReturn(errEntry -> errEntry.getKey().isAssignableFrom(errType))
+                .map(Map.Entry::getValue)
+                .orElse(null);
+
+        return (T) err;
     }
 
     /**
diff --git a/uno-core/src/main/java/cc/allio/uno/core/datastructure/tree/TreeSupport.java b/uno-core/src/main/java/cc/allio/uno/core/datastructure/tree/TreeSupport.java
index 6c765da6..d7ceddc6 100644
--- a/uno-core/src/main/java/cc/allio/uno/core/datastructure/tree/TreeSupport.java
+++ b/uno-core/src/main/java/cc/allio/uno/core/datastructure/tree/TreeSupport.java
@@ -170,7 +170,7 @@ static <T, R> Stream<R> doExpandFn(Collection<T> forest, MethodFunction<T,Collec
                     String fieldName = childrenFunc.getFieldName();
                     Collection<T> children = BeanWrapper.getValue(element, fieldName, Collection.class);
                     if (CollectionUtils.isNotEmpty(children)) {
-                        return doExpandFn(forest, childrenFunc, transfer);
+                        return doExpandFn(children, childrenFunc, transfer);
                     }
                     return Stream.of(transfer.apply(element));
                 });