Code for a SharePoint Framework property pane with multiple pages. See http://cob-sp.com/SPFx-WP-Props1

WebPartPropetyPane_MultiplePages.ts

protected getPropertyPaneConfiguration(): IPropertyPaneConfiguration {
    return {
      pages: [
        {
          header: {
            description: "Basic settings"
          },
          groups: [
            {
              groupName: "Look and feel",
              groupFields: [
                PropertyPaneTextField('description', {
                  label: "Web part description"
                }),
                PropertyPaneTextField('noResultsMsg', {
                  label: "No results message"
                })
              ]
            }
          ]
        },
        {
          header: {
            description: "Advanced settings"
          },
          groups: [
            {
              groupName: "Search configuration",
              groupFields: [
                PropertyPaneTextField('searchTag', {
                  label: "Tag to search for"
                }),
                PropertyPaneDropdown('displayType', {
                  label: "Display type",
                  options: [
                    { key: '2Cols', text: 'Two columns' },
                    { key: '3Cols', text: 'Three columns' },
                    { key: 'Horizontal', text: 'Horizontal'}
                  ],
                  selectedKey: '3Cols'
                 }
                })
              ]
            }
          ]
        }
      ]
    };
  }
}