05C05 05C50 3 05C20 2 05C40 2 05C60 2 05C63 2 15A18 2 20B25 2 20E08 2 20F28 2 20F32 2 20H05 2 20M18 2 20M20 2 Wreath product 2 automorphisms of trees 2 classification 2 co-neighbour vertices 2 congruence subgroups 2 conjugate Laplacian matrix 2 finite groups acting on a tree 2 finite inverse symmetric semigroup 2 homogenous rooted trees 2 local isometry 2 modular group 2 partial automorphism 2 rooted tree 2 rooted trees 2 suborbital graphs 2 ultrametrics 2