public TraceGraph(Collection<Span> spans){
  this.spansByParent=new SpansByParent(spans);
  this.spansByTracerId=new SpansByTracerId(spans);
}

public TraceGraph ( Collection < Span > spans ) { this . spansByParent = new SpansByParent ( spans ) ; this . spansByTracerId = new SpansByTracerId ( spans ) ; }
create a new tracegraph
