branch-nodes.js

const parentItems:TreeItem[] = [];
  parentKeys.forEach( ( v:string ):void=>{
    let parts = v.split( `-` );
    while ( uniqueIds.has( lastId ) ) {
      lastId += 1;
    }
    uniqueIds.add( lastId );
    let name = parts.pop() || ``;
    parentItems.push( {
      id: lastId,
      key: v,
      name,
      parentKey: parts.join( `-` )
    } );
  } );