adaptive mesh display

Question

does anyone know how to display an adaptively refined mesh?
when plotting the mesh after adaptive solve, I just see the initially defined mesh (of course):

from dolfin import *
mesh = UnitSquareMesh(4, 4)
V = FunctionSpace(mesh , "CG", 1)
u = TrialFunction(V); v = TestFunction(V); u_h = Function(V)

a = dot(grad(u), grad(v))dx
L = vdx
bc = DirichletBC(V, 0.0, "near(x[0], 0.0)")

M = u_h*dx
solve(a == L, u_h, bc, tol=1e-4, M=M)

plot(mesh); interactive()

Answer 1

mesh.root_node() # the coarsest one
mesh.leaf_node() # the finest one

and similarly for other refined quantities.

Comments

How to get the mesh between the coarsest one and the finest one, and similarly for other refined quantities?
Thanks very much in advance.

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object.parent()
object.child()