使用jQuery递归更改元素类型，为什么它部分工作？

Source node:

 <div class="tree">
    <div class="item"><!-- replaced OK -->
        <a href class="toggle">+</a>
        <a href class="name">Name</a>
        <div class="collapse">
            <div class="item"><!-- this wouldn't be replaced ?! --></div>
        </div>
    </div>
    <div class="item"></div><!-- replaced OK -->
</div>
 <div class="tree">
    <div cla