element.appendChild(container);

Пример CSS для стилизации дерева:

```css
.tree-node {
    position: relative;
    padding-left: 20px;
}

.tree-node::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    border-left: 1px solid #000;
}

.tree-node:first-child::before {
    display: none;
}

.tree-node:last-child {
    padding-bottom: 10px;
}

.tree-node:last-child::before {
    height: 10px;
    top: auto;
    bottom: 0;
}

.tree-children {
    margin-left: 20px;
}