OpenGL and VTK compatibility

I am still a little confused. This is my current class which populates an OpenGL widget in PyQt5. (There’s an additional method that reads rotation data over serial, but it’s not included.) How would I be able to draw the STL using what I currently have? Currently I draw a cube within paintGL.

class OpenGLWidget(QOpenGLWidget):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.roll = 0.0
        self.pitch = 0.0
        self.yaw = 0.0

    def initializeGL(self):
        glEnable(GL_DEPTH_TEST)
        glClearColor(0.0, 0.0, 0.0, 1.0)

    def resizeGL(self, width, height):
        glViewport(0, 0, width, height)
        glMatrixMode(GL_PROJECTION)
        glLoadIdentity()
        aspect_ratio = width / height
        gluPerspective(45, aspect_ratio, 0.1, 100.0)
        glMatrixMode(GL_MODELVIEW)

    def paintGL(self):
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
        glLoadIdentity()
        glTranslatef(0.0, 0.0, -10.0)
        glRotatef(self.pitch, -1.0, 0.0, 0.0)
        #glRotatef(self.yaw, 0.0, 1.0, 0.0)
        glRotatef(self.roll, 0.0, 0.0, -1.0)

        # Cube
        glBegin(GL_QUADS)

        glColor3f(1.0, 0.0, 0.0)
        glVertex3f(1.0, 1.0, -1.0)
        glVertex3f(-1.0, 1.0, -1.0)
        glVertex3f(-1.0, 1.0, 1.0)
        glVertex3f(1.0, 1.0, 1.0)

        glColor3f(0.0, 1.0, 0.0)
        glVertex3f(1.0, -1.0, 1.0)
        glVertex3f(-1.0, -1.0, 1.0)
        glVertex3f(-1.0, -1.0, -1.0)
        glVertex3f(1.0, -1.0, -1.0)

        glColor3f(0.0, 0.0, 1.0)
        glVertex3f(1.0, 1.0, 1.0)
        glVertex3f(-1.0, 1.0, 1.0)
        glVertex3f(-1.0, -1.0, 1.0)
        glVertex3f(1.0, -1.0, 1.0)

        glColor3f(1.0, 1.0, 0.0)
        glVertex3f(1.0, -1.0, -1.0)
        glVertex3f(-1.0, -1.0, -1.0)
        glVertex3f(-1.0, 1.0, -1.0)
        glVertex3f(1.0, 1.0, -1.0)

        glColor3f(0.0, 1.0, 1.0)
        glVertex3f(-1.0, 1.0, 1.0)
        glVertex3f(-1.0, 1.0, -1.0)
        glVertex3f(-1.0, -1.0, -1.0)
        glVertex3f(-1.0, -1.0, 1.0)

        glColor3f(1.0, 0.0, 1.0)
        glVertex3f(1.0, 1.0, -1.0)
        glVertex3f(1.0, 1.0, 1.0)
        glVertex3f(1.0, -1.0, 1.0)
        glVertex3f(1.0, -1.0, -1.0)

        glEnd()

        self.update()