diff --git a/bench/algorithm/binarytrees/2.swift b/bench/algorithm/binarytrees/2.swift
new file mode 100644
index 000000000..dc2d05e8d
--- /dev/null
+++ b/bench/algorithm/binarytrees/2.swift
@@ -0,0 +1,64 @@
+import Foundation
+
+let minDepth = 4
+let maxDepth: Int = {
+    if CommandLine.argc <= 1 { return 10 }
+    return max(minDepth + 2, Int(CommandLine.arguments[1]) ?? 10)
+}()
+
+let stretchDepth = maxDepth + 1
+print("stretch tree of depth \(stretchDepth)\t check: \(Tree(depth: stretchDepth).check())")
+
+let longLivedTree = Tree(depth: maxDepth)
+let nResults = (maxDepth - minDepth) / 2 + 1
+
+for i in 0..<nResults {
+    let depth = i * 2 + minDepth
+    let n = 1 << (maxDepth - depth + minDepth)
+
+    var chk = 0
+    for _ in 0..<n {
+        chk += Tree(depth: depth).check()
+    }
+    print("\(n)\t trees of depth \(depth)\t check: \(chk)")
+}
+
+print("long lived tree of depth \(maxDepth)\t check: \(longLivedTree.check())")
+
+struct Tree {
+    struct Node {
+        var left: Int
+        var right: Int
+    }
+
+    private static let none: Int = -1
+    private var nodes: [Node] = []
+    private var root: Int = none
+
+    init(depth: Int) {
+        let total = (1 << (depth + 1)) - 1
+        guard total > 0 else { return }
+
+        nodes = Array(repeating: Node(left: Self.none, right: Self.none), count: total)
+        root = 0
+
+        for i in 0..<total {
+            let l = 2 * i + 1
+            let r = l + 1
+            if l < total { nodes[i].left = l }
+            if r < total { nodes[i].right = r }
+        }
+    }
+
+    func check() -> Int {
+        let span = nodes.span
+        return _check(index: root, span: span)
+    }
+
+    private func _check(index: Int, span: Span<Node>) -> Int {
+        if index == Self.none { return 0 }
+        let node = span[Int(index)]
+        return 1 + _check(index: node.left, span: span)
+            + _check(index: node.right, span: span)
+    }
+}
diff --git a/bench/bench_swift.yaml b/bench/bench_swift.yaml
index 1273c20b7..4fedb7da8 100644
--- a/bench/bench_swift.yaml
+++ b/bench/bench_swift.yaml
@@ -6,6 +6,7 @@ problems:
   - name: binarytrees
     source:
       - 1.swift
+      - 2.swift
   - name: nbody
     source:
       - 7.swift
@@ -30,7 +31,7 @@ environments:
   - os: linux
     compiler: swift
     version: latest
-    docker: swift:jammy
+    docker: swift:6.2.0-slim
     include: swift
     include_sub_dir: Sources/app
     build: swift build --static-swift-stdlib -c release -v -Xswiftc -Ounchecked