Enum GlyphType

var 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);