Tree position on random Terrain (y axis)

So - I have random generated terrain - here's fragment of my script:

 public void GenerateHeights(Terrain terrain, float tileSize)
 {

     float[,] heights = new float[terrain.terrainData.heightmapWidth, terrain.terrainData.heightmapHeight];
     
     for (int i = 0; i < terrain.terrainData.heightmapWidth; i++)
     {
         for (int k = 0; k < terrain.terrainData.heightmapHeight; k++)
         {

             float MapFix = terrain.terrainData.size.x/terrain.terrainData.heightmapWidth;
             
             float MapFix2 = terrain.terrainData.size.z/terrain.terrainData.heightmapHeight;


             heights[i, k] = Mathf.PerlinNoise(((float)i / (float)terrain.terrainData.heightmapWidth) * tileSize, ((float)k / (float)terrain.terrainData.heightmapHeight) * tileSize)/randomNumber;


             if(Random.Range(0, 1000)==1){

             Instantiate(tree, new Vector3 (k*MapFix,heights[i, k],i*MapFix2), Quaternion.identity);
             }
         }
     }
     
     terrain.terrainData.SetHeights(0, 0, heights);


 }

And - X and Z is ok, but Y is 0. How to fix this?