Enum GlyphType

const body =
    DocumentApp.getActiveDocument().getActiveTab().asDocumentTab().getBody();

// Insert at list item, with the default nesting level of zero.
body.appendListItem('Item 1');

// Append a second list item, with a nesting level of one, indented one inch.
// The two items have different bullet glyphs.
body.appendListItem('Item 2')
    .setNestingLevel(1)
    .setIndentStart(72)
    .setGlyphType(DocumentApp.GlyphType.SQUARE_BULLET);