<table class="table table-striped table-header-rotated" *ngIf="product.vin == old_VIN">
     <!-- Что-то такое? -->
            <thead>
              <tr>
                <!-- First column header is not rotated -->
                <th></th>
                <!-- Following headers are rotated -->
                <th class="rotate-45" *ngFor="let product of filter_product; let i=index;"><div><span>Договор {{i+1}}</span></div></th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td class="row-header">Договор №</td>
                <td *ngFor="let product of filter_product;">{{product.treaty_number}</td>
              </tr>
                 <tr>
                <td class="row-header">Улучшение условий</td>
                <td *ngFor="let product of filter_product;">{{product.improving_conditions}</td>
              </tr>
             <tr>
            <td class="row-header">VIN</td>
            <td *ngFor="let product of filter_product;">{{product.vin}}</td>
          </tr>
            </tbody>
          </table>

<table class="table table-striped table-header-rotated">
         <!-- Что-то такое? -->
                <thead>
                  <tr>
                    <!-- First column header is not rotated -->
                    <th></th>
                    <!-- Following headers are rotated -->
                    <th><div><span>Договор 1</span></div></th>
                    <th><div><span>Договор 2</span></div></th>
                  </tr>
                </thead>
                <tbody>
                  <tr>
                    <td class="row-header">Договор №</td>
                    <td>2310-22</td>
                    <td>1314-82</td>
                  </tr>
                     <tr>
                    <td class="row-header">Улучшение условий</td>
                    <td>Нет</td>
                    <td>Нет</td>
                  </tr>
                 <tr>
                <td class="row-header">VIN</td>
                <td>X23254FSFS43</td>
                <td>X23254FSFS43</td>
              </tr>
                </tbody>
              </table>

@Pipe({name: 'groupBy'})
export class GroupByPipe implements PipeTransform {
  transform(value: Array<any>, field: string): Array<any> {
    const groupedObj = value.reduce((prev, cur)=> {
      if(!prev[cur[field]]) {
        prev[cur[field]] = [cur];
      } else {
        prev[cur[field]].push(cur);
      }
      return prev;
    }, {});
    return Object.keys(groupedObj).map(key => ({ key, value: groupedObj[key] }));
  }
}

table.table.table-striped.table-header-rotated(*ngFor="let products of filter_product | groupBy:'vin'")
    thead
        tr
            th
            th(*ngFor="let product of products.value; let i=index;") Договор {{ i + 1}}
    tbody
        tr
            td.row-header Договор №
            td(*ngFor="let product of products.value") {{ product.treaty_number }}
        tr
            td.row-header Улучшение условий
            td(*ngFor="let product of products.value") {{ product.improving_conditions }}
        tr
            td.row-header VIN
            td(*ngFor="let product of products.value") {{ product.vin }}