$MOD=10**9+7

class Combi
  def initialize(max_n, mod = 10**9+7)
      @mod = mod
      @max_n = max_n

      @fac = Array.new(@max_n+1)
      @inv = Array.new(@max_n+1)
      @finv = Array.new(@max_n+1)

      @fac[0] = @fac[1] = 1
      @finv[0] = @finv[1] = 1
      @inv[1] = 1
      2.upto(@max_n) do |i|
          @fac[i] = @fac[i-1] * i % @mod
          @inv[i] = @mod - @inv[@mod%i] * (@mod/i) % @mod
          @finv[i] = @finv[i-1] * @inv[i] % @mod
      end
  end

  def nCk(n,k)
    return 0 if(k<0 || k>n) 
    @fac[n] * @finv[n - k] * @finv[k] % @mod
  end
  def nPk(n,k)
    return 0 if(k<0 || k>n)
    @fac[n] * @finv[n - k] % @mod
  end
end

$combi = Combi.new(1000000)

n,k=gets.chomp.split.map(&:to_i)
edge = Array.new(n+1).map{Array.new()}

(n-1).times do
  a,b=gets.chomp.split.map(&:to_i)
  edge[a] << b;
  edge[b] << a;
end

def dfs(parent, n, edge, k)
  return 1 if edge[n].size == 1

  ret = $combi.nPk(k-2,edge[n].size-1)

  edge[n].each do |i|
    next if i == parent
    ret = ret * dfs(n,i,edge,k)
    ret %= $MOD
  end
  ret
end

ans=$combi.nPk(k,edge[1].size+1)

edge[1].each do |i|
  ans*=dfs(1,i,edge,k)
  ans%=$MOD
end
puts ans

