flex布局

 .tree-bar {
            margin-top: 10px;
            width: 100%;
            display: flex;
            flex-direction: column;
            #exptree, #comptree {
                flex: 1;
            }
            .add-exam {
                text-align: center;
                border-top: 1px solid #ddd;
                line-height: 50px;
                height: 50px;
                font-size: 15px;
                background-color: #fff;
                color: #666;
                text-decoration: none;
            }
            a:hover {
                color: #337ab7;
            }
        }