Flask sqlalchemy：尝试创建html树

我想在我的Flask应用程序中创建以下形式的HTML树：

测验 A. ab 交流电 B 卑诗省 直流电

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我有完全相同的问题。。。我设法用以下方法解决了这个问题：

test_data = Test.query.all()

newest = "<ul class='nav nav-list'>"
for i in test_data:
    newest = newest + "<li><label class='tree-toggler nav-header'> <i class='icon-plus-sign'></i>" + str(i.sec) + " </label><ul class='nav nav-list tree'>" 
    x = Test.query.filter_by(sec = i.sec).group_by(Test.secsec)
    for f in x:
            newest = newest + "<li><label class='tree-toggler nav-header'> <i class='icon-plus-sign'></i>" + str(f.secsec) + "</label><ul class='nav nav-list tree'>"
            y = Test.query.filter_by(sec = i.sec, secsec = f.secsec ).group_by(Test.spn)
            for n in y:
                    newest = newest + "<li><input type='text' class='spn' value = " + str(n.part) + " readonly><input type='submit' value='add to list' class='btn submit' /></li>"
            newest = newest + "</ul></li>"
    newest = newest + "</ul></li>"
newest = newest + "</ul>ul class='nav nav-list'>"

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但不幸的是，运行脚本需要花费很长时间

请在问题中详细说明所有崩溃的含义。