#include<stdio.h>
#include<stdlib.h>
#include<stdint.h>
#include<inttypes.h>
#include<string.h>
#include<math.h>

typedef int32_t i32;
typedef int64_t i64;

typedef struct directed_edge {
  int32_t vertex;
  int32_t next;
} graph_edge;

typedef struct directedGraph {
  graph_edge *edge;
  int32_t *start;
  int32_t pointer;
  int32_t vertex_num;
  int32_t edge_max_size;
} graph;

graph* new_graph (const int vertex_num) {
  graph *g = (graph *) calloc (1, sizeof (graph));
  g->edge = (graph_edge *) calloc (1, sizeof (graph_edge));
  g->start = (int32_t *) calloc (vertex_num, sizeof (int32_t));
  g->pointer = 0;
  g->vertex_num = vertex_num;
  g->edge_max_size = 1;
  for (int32_t i = 0; i < vertex_num; ++i) {
    g->start[i] = -1;
  }
  return g;
}

void free_graph (graph *g) {
  free (g->edge);
  free (g->start);
  free (g);
  return;
}

void clear_graph (graph *g) {
  g->pointer = 0;
  for (int32_t i = 0; i < g->vertex_num; ++i) {
    g->start[i] = -1;
  }
}

void add_edge (graph *g, int32_t from, int32_t to) {
  if (g->pointer == g->edge_max_size) {
    g->edge_max_size *= 2;
    g->edge = (graph_edge *) realloc (g->edge, sizeof (graph_edge) * g->edge_max_size);
  }
  g->edge[g->pointer] = (graph_edge) {to, g->start[from]};
  g->start[from] = g->pointer++;
}

void BFS_graph (graph *g, int32_t src) {
  int32_t *q = (int32_t *) calloc (g->vertex_num, sizeof (int32_t));
  uint8_t *used = (uint8_t *) calloc (g->vertex_num, sizeof (uint8_t));
  int32_t front = 0;
  int32_t last = 0;
  used[src] = 1;
  q[last++] = src;
  while (front < last) {
    const int32_t v = q[front++];
    for (int32_t p = g->start[v]; p != -1; p = g->edge[p].next) {
      const int32_t u = g->edge[p].vertex;
      //hoge
      if (!used[u]) {
        used[u] = 1;
        q[last++] = u;
      }
    }
  }
  free(q);
  free(used);
}

#define MAX(a,b) ((a)>(b)?(a):(b))
#define MIN(a,b) ((a)<(b)?(a):(b))
#define ABS(a) ((a)>(0)?(a):-(a))
#define ALLOC(size,type) ((type*)calloc((size),sizeof(type)))
#define SORT(a,num,cmp) qsort((a),(num),sizeof(*(a)),cmp)

const i32 mod = 1000000007;

#define ADD(x, a) do{(x) += (a); if ((x) >= mod) (x) -= mod;} while (0)
#define SUB(x, a) do{(x) += mod - (a); if ((x) >= mod) (x) -= mod;} while (0)
#define MUL(x, a) do{(x) = (i64) (x) * (a) % mod;} while (0)
#define DIV(x, a) MUL(x, inv(a))

i32 mod_pow (i32 r, i32 n) {
  i32 t = 1;
  i32 s = r;
  while (n > 0) {
    if (n & 1) t = (i64) t * s % mod;
    s = (i64) s * s % mod;
    n >>= 1;
  }
  return t;
}

i32 inv (i32 a) {
  return mod_pow (a, mod - 2);
}

i32 *fact = NULL;
i32 *iFact = NULL;
void init_fact (const i32 n) {
  fact = (i32 *) calloc (n + 1, sizeof (i32));
  fact[0] = 1;
  for (i32 i = 1; i <= n; ++i) {
    fact[i] = (i64) i * fact[i - 1] % mod;
  }
  iFact = (i32 *) calloc (n + 1, sizeof (i32));
  iFact[n] = inv (fact[n]);
  for (i32 i = n - 1; i >= 0; --i) {
    iFact[i] = (i64) (i + 1) * iFact[i + 1] % mod;
  }
}

i32 perm (i32 n, i32 k) {
  if (!(0 <=k && k <= n)) return 0;
  return (i64) fact[n] * iFact[n - k] % mod;
}

i32 comb (i32 n, i32 k) {
  if (!(0 <= k && k <= n)) return 0;
  return (i64) fact[n] * iFact[k] % mod * iFact[n - k] % mod;
}

i32 calc (i32 v, graph *g, i32 k, uint8_t *used) {
  used[v] = 1;
  i32 cnt = 0;
  for (i32 p = g->start[v]; p != -1; p = g->edge[p].next) {
    i32 u = g->edge[p].vertex;
    if (used[u]) continue;
    cnt++;
  }
  i32 ans = perm (k - 2, cnt);
  for (i32 p = g->start[v]; p != -1; p = g->edge[p].next) {
    i32 u = g->edge[p].vertex;
    if (used[u]) continue;
    ans = (i64) ans * calc (u, g, k, used) % mod;
  }
  return ans;
}

void run (void) {
  i32 n, k;
  scanf ("%" SCNi32 "%" SCNi32, &n, &k);
  if (n == 1) {
    printf ("%" PRIi32 "\n", k);
    return;
  }
  i32 *d = ALLOC (n, i32);
  graph *g = new_graph (n);
  for (i32 i = 1; i < n; ++i) {
    i32 a, b;
    scanf ("%" SCNi32 "%" SCNi32, &a, &b);
    a--; b--;
    add_edge (g, a, b);
    add_edge (g, b, a);
    d[a]++;
    d[b]++;
  }
  init_fact (n + k);
  uint8_t *used = ALLOC (n, uint8_t);
  for (i32 i = 0; i < n; ++i) {
    if (d[i] == 1) {
      used[i] = 1;
      i32 u = g->edge[g->start[i]].vertex;
      i32 ans = (i64) k * (k - 1) * calc (u, g, k, used) % mod;
      printf ("%" PRIi32 "\n", ans);
      break;
    }
  }
}

int main (void) {
  run();
  return 0;
}


Measured memory_bytes: 9728