Raw HTML Table

HTML

<table>
    <thead>
        <tr>
            <th>Layer 1</th>
            <th>Layer 2</th>
            <th>Layer 3</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td rowspan=4>L1 Name</td>
            <td rowspan=2>L2 Name A</td>
            <td>L3 Name A</td>
        </tr>
        <tr>
            <td>L3 Name B</td>
        </tr>
        <tr>
            <td rowspan=2>L2 Name B</td>
            <td>L3 Name C</td>
        </tr>
        <tr>
            <td>L3 Name D</td>
        </tr>
    </tbody>
</table>

CSS

table {
    border-collapse: collapse;
}

table, th, td {
    border: 1px solid black;
}