MeshCollider has different shape than MeshFilter


I am generating mesh and then I am assigning it to MeshCollider’s sharedMesh. My problem is showed right on the attached picture. The shape of purple object is exactly what I wanted. However mesh collider has a different shape, and I expected it to have the same shape as object has.

This is the code of generating:

public class MeshGeneratortTest : MonoBehaviour {
    public int width = 10;
    void Start() {
          Mesh mesh = GetComponent<MeshFilter>().mesh;
          mesh.vertices = new Vector3[] {new Vector3(0, 0, 0), new Vector3(0, 0, width), new Vector3(20, 2, 0), new Vector3(20, 2, width), 
								 	   	 new Vector3(34, 11, 0), new Vector3(34, 11, width) };
          mesh.uv = new Vector2[] {new Vector2(0, 0), new Vector2(0, 1), new Vector2(1, 1)};
          mesh.triangles = new int[] {0,1,2,   1,2,3,   2,3,4,   3,4,5, };
          GetComponent<MeshCollider>().sharedMesh = mesh;

I know I am not editing tangents of vertices, but from what I read i understood that’s used mainly just for some lighting systems and shaders, Am I right ?
Could someone tell me what I messed up or just push me to right direction ?

// Edit:
I noticed that when I pause the game and take a look at collider mesh in inspector view, it looks right. However in real, in scene view, there are 2 extra triangles on collider connecting both side of object. Are there some specials rules for meshes ? So maybe unity is trying to fix something I did wrong when I initialised vertices and triangles ?

Thank you very much.

You’re making it a convex mesh, hence what you’re getting is expected behavior.