#include <bits/stdc++.h>
#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC optimize("Ofast")
#pragma GCC optimize("inline")
#pragma GCC optimize("-fgcse")
#pragma GCC optimize("-fgcse-lm")
#pragma GCC optimize("-fipa-sra")
#pragma GCC optimize("-ftree-pre")
#pragma GCC optimize("-ftree-vrp")
#pragma GCC optimize("-fpeephole2")
#pragma GCC optimize("-ffast-math")
#pragma GCC optimize("-fsched-spec")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("-falign-jumps")
#pragma GCC optimize("-falign-loops")
#pragma GCC optimize("-falign-labels")
#pragma GCC optimize("-fdevirtualize")
#pragma GCC optimize("-fcaller-saves")
#pragma GCC optimize("-fcrossjumping")
#pragma GCC optimize("-fthread-jumps")
#pragma GCC optimize("-funroll-loops")
#pragma GCC optimize("-fwhole-program")
#pragma GCC optimize("-freorder-blocks")
#pragma GCC optimize("-fschedule-insns")
#pragma GCC optimize("inline-functions")
#pragma GCC optimize("-ftree-tail-merge")
#pragma GCC optimize("-fschedule-insns2")
#pragma GCC optimize("-fstrict-aliasing")
#pragma GCC optimize("-fstrict-overflow")
#pragma GCC optimize("-falign-functions")
#pragma GCC optimize("-fcse-skip-blocks")
#pragma GCC optimize("-fcse-follow-jumps")
#pragma GCC optimize("-fsched-interblock")
#pragma GCC optimize("-fpartial-inlining")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("-freorder-functions")
#pragma GCC optimize("-findirect-inlining")
#pragma GCC optimize("-fhoist-adjacent-loads")
#pragma GCC optimize("-frerun-cse-after-loop")
#pragma GCC optimize("inline-small-functions")
#pragma GCC optimize("-finline-small-functions")
#pragma GCC optimize("-ftree-switch-conversion")
#pragma GCC optimize("-foptimize-sibling-calls")
#pragma GCC optimize("-fexpensive-optimizations")
#pragma GCC optimize("-funsafe-loop-optimizations")
#pragma GCC optimize("inline-functions-called-once")
#pragma GCC optimize("-fdelete-null-pointer-checks")
using namespace std;
const long long mo = 1e9 + 7;
template <typename _T>
void read(_T &x) {
  _T f = 1;
  x = 0;
  char s = getchar();
  while (s > '9' || s < '0') {
    if (s == '-') f = -1;
    s = getchar();
  }
  while (s >= '0' && s <= '9') {
    x = (x << 3) + (x << 1) + (s ^ 48);
    s = getchar();
  }
  x *= f;
}
int n, k, head[105], tot;
long long dp[105][105], tmp[105], ans;
struct edge {
  int v, nxt;
} e[105 << 1];
void addEdge(int u, int v) {
  e[++tot] = (edge){v, head[u]};
  head[u] = tot;
}
void dfs(int x, int fa) {
  dp[x][0] = dp[x][k + 1] = 1;
  for (int i = head[x]; i; i = e[i].nxt) {
    int v = e[i].v;
    if (v == fa) continue;
    dfs(v, x);
    for (int j = 0; j <= 2 * k; j++) tmp[j] = 0;
    for (int j1 = 0; j1 <= 2 * k; j1++)
      for (int j2 = 0; j2 <= 2 * k; j2++)
        if (j1 + j2 <= 2 * k)
          (tmp[min(j1, j2 + 1)] += dp[x][j1] * dp[v][j2] % mo) %= mo;
        else
          (tmp[max(j1, j2 + 1)] += dp[x][j1] * dp[v][j2] % mo) %= mo;
    for (int j = 0; j <= 2 * k; j++) dp[x][j] = tmp[j];
  }
}
signed main() {
  read(n);
  read(k);
  for (int i = 1; i < n; i++) {
    int u, v;
    read(u);
    read(v);
    addEdge(u, v);
    addEdge(v, u);
  }
  dfs(1, 0);
  for (int i = 0; i <= k; i++) (ans += dp[1][i]) %= mo;
  printf("%lld\n", ans);
  return 0;
}
