import sys

# sys.setrecursionlimit(1000005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = (1 << 63)-1
# inf = (1 << 31)-1
md = 10**9+7
# md = 998244353

n, k = LI()
to = [[] for _ in range(n)]
for _ in range(n-1):
    u, v = LI()
    to[u].append(v)
    to[v].append(u)

parent, depth, vis = [-1]*n, [0]*n, [0]*n

def dfs(root):
    uu = []
    vis[root] = 1
    stack = [root]
    while stack:
        iu = stack.pop()
        i, u = divmod(iu, n)
        if i == 0:
            uu.append(u)
        # care to's format
        while i < len(to[u]) and vis[to[u][i]]: i += 1
        if i < len(to[u]):
            stack.append((i+1)*n+u)
            # care to's format
            v = to[u][i]
            vis[v] = 1
            stack.append(v)
            parent[v] = u
            depth[v] = depth[u]+1

    return uu

uu = dfs(0)
size = [1]*n
for u in uu[:0:-1]:
    p = parent[u]
    size[p] += size[u]

def merge(p, u):
    m = min(k+1, len(dp[p])+len(dp[u])-1)
    cur = [0]*m
    for s, c in enumerate(dp[p]):
        for t, d in enumerate(dp[u]):
            if s+t >= m: break
            cur[s+t] += c*d%md
            cur[s+t] %= md
    dp[p] = cur

dp = [[1] for _ in range(n)]
for u in uu[::-1]:
    if len(dp[u]) <= k: dp[u].append(1)
    p = parent[u]
    merge(p, u)

print(dp[0][k])