TreeMain

using UnityEngine;
using System.Collections;

public class TreeMain : MonoBehaviour {

    private GameObject tree;
    private bool callOnce;

    public int treeHealth = 5;
    public int speed = 2;

    void Start ()
    {
        callOnce = false;
        tree = this.gameObject;
    }

    void Update ()
    {
        if(treeHealth == 1)
        {
            callOnce = true;
        }

        if((treeHealth <= 0) && (callOnce == true))
        {
            tree.AddComponent<Rigidbody>();
            GetComponent<Rigidbody>().isKinematic = false;
            GetComponent<Rigidbody>().AddForce(transform.forward * speed, ForceMode.Impulse);
            DestroyTree();
            Destroy(tree);
            callOnce = false;
        }
    }

    IEnumerator DestroyTree()
    {
        yield return new WaitForSeconds(7);
    }
}