Let G = (V, E), V = {v1, v2,..., vn}, be a simple graph without isolated
vertices, with the sequence of vertex degrees d1 ? d2 ?...? dn > 0, di =
d(vi). If vertices vi and vj are adjacent in G, we write i ~ j, otherwise we
write i ~/ j. The inverse degree topological index of G is defined to be
ID(G) = ?ni=1 1/di = ? i~j (1/d2i + 1/d2j), and the inverse degree
coindex ?ID(G) = ? i~/j(1/d2i + 1/d2j). We obtain a number of inequalities
which determine bounds for the ID(G) and ?ID(G) when G is a tree.