#define trigpin 9//set trigpin
#define echopin 8//set echopin
#include <Servo.h>
Servo myservo;// declare servo name type servo
  int duration, distance;//declare variable for unltrasonic sensor

const int ledPinR=13;
const int ledPinB=12;
const int ledPinp=11;

void setup() {
  Serial.begin(9600);
  pinMode(trigpin, OUTPUT);
 
  pinMode(echopin, INPUT);
  myservo.attach(A0);// attach your servo

   pinMode(ledPinB,OUTPUT);
  
   pinMode(ledPinR,OUTPUT);
   pinMode(ledPinp,OUTPUT);
myservo.writeMicroseconds(1500);
  // put your setup code here, to run once:
}
void loop() {

  
  myservo.write(40);// always set servo to 90 to position it to the middle
//ultrasonic code 
 digitalWrite(trigpin,HIGH);
  _delay_ms(500);
  digitalWrite(trigpin, LOW);
  
  duration=pulseIn(echopin,HIGH); 
  distance=(duration/2)/29.1; 

 if(distance <=110 && distance>=70)
 {digitalWrite(ledPinR,LOW);
  digitalWrite(ledPinB,LOW);

   digitalWrite(ledPinp,LOW);
   
  myservo.write(0); //servo rotates at full speed to the right
  delay(600);
}

else if (distance <70 && distance >40)
{
 digitalWrite(ledPinR,HIGH);
  digitalWrite(ledPinB,LOW);
  
     digitalWrite(ledPinp,LOW);
  myservo.write(0); //servo rotates at full speed to the right
  delay(600);
}

else if (distance <=40 && distance>=15)
{
 digitalWrite(ledPinR,HIGH);
  digitalWrite(ledPinB,HIGH);
     digitalWrite(ledPinp,LOW);      
  myservo.write(0); //servo rotates at full speed to the right
  delay(600);
}

else if (distance <15)
{
 digitalWrite(ledPinR,HIGH);
  digitalWrite(ledPinB,HIGH);
  digitalWrite(ledPinp,HIGH);

  myservo.write(0); //servo rotates at full speed to the right
  delay(600);
}
else{ digitalWrite(ledPinR,LOW);
  digitalWrite(ledPinB,LOW);
     digitalWrite(ledPinp,LOW);
       digitalWrite(ledPinB,LOW);
 myservo.write(40);// else servo stays at 90 degree angle.
  delay(600);
  }
  Serial.print("cm"); //print distance unit cm
Serial.println(distance);//distance
 
  // put your main code here, to run repeatedly:
}

References: 

https://www.youtube.com/watch?v=4kWS1q8zFFc

http://wallpapers9.org/2015-christmas-tree-lights/