How do you fix speed tree rotation?

I know this is an old question but in blender the z axis is up and in unity the z axis is forward, that is why things are rotated -90 degrees. I found a script that if you put in your project will fix blender imports. Just simply re-import everything with this script in your project, call it BlenderAssetProcessor.cs

 using UnityEngine;
 using UnityEditor;
 using System.Collections;
 using System.IO;
 using System.Linq;
 public class BlenderAssetProcessor : AssetPostprocessor {
     public void OnPostprocessModel(GameObject obj) {
         //only perform corrections with blender files
         ModelImporter importer = assetImporter as ModelImporter;
         if (Path.GetExtension (importer.assetPath) == ".blend") {
             RotateObject (obj.transform);
         }
         //Don't know why we need this...
         //Fixes wrong parent rotation
         obj.transform.rotation = Quaternion.identity;
     }
     //recursively rotate a object tree individualy
     private void RotateObject(Transform obj) {
         Vector3 objRotation = obj.eulerAngles;
         objRotation.x += 90f;
         obj.eulerAngles = objRotation;
         //if a meshFilter is attached, we rotate the vertex mesh data
         MeshFilter meshFilter = obj.GetComponent (typeof(MeshFilter)) as MeshFilter;
         if (meshFilter) {
             RotateMesh (meshFilter.sharedMesh);
         }
         //do this too for all our children
         //Casting is done to get rid of implicit downcast errors
         foreach (Transform child in obj) {
             RotateObject (child);
         }
     }
     //"rotate" the mesh data
     private void RotateMesh(Mesh mesh) {
         int index = 0;
         //switch all vertex z values with y values
         Vector3[] vertices = mesh.vertices;
         for (index = 0; index < vertices.Length; index++) {
             vertices [index] = new Vector3 (vertices [index].x, vertices [index].z, vertices [index].y);
         }
         mesh.vertices = vertices;
         //for each submesh, we invert the order of vertices for all triangles
         //for some reason changing the vertex positions flips all the normals???
         for (int submesh = 0; submesh < mesh.subMeshCount; submesh++) {
             int[] triangles = mesh.GetTriangles (submesh);
             for (index = 0; index < triangles.Length; index += 3) {
                 int intermediate = triangles [index];
                 triangles [index] = triangles [index + 2];
                 triangles [index + 2] = intermediate;
             }
             mesh.SetTriangles (triangles, submesh);
         }
         //recalculate other relevant mesh data
         mesh.RecalculateNormals ();
         mesh.RecalculateBounds ();
     }
 }