macro_rules ! input { ( source = $ s : expr , $ ( $ r : tt ) * ) => { let mut iter = $ s . split_whitespace ( ) ; input_inner ! { iter , $ ( $ r ) * } } ; ( $ ( $ r : tt ) * ) => { let s = { use std :: io :: Read ; let mut s = String :: new ( ) ; std :: io :: stdin ( ) . read_to_string ( & mut s ) . unwrap ( ) ; s } ; let mut iter = s . split_whitespace ( ) ; input_inner ! { iter , $ ( $ r ) * } } ; }
macro_rules ! input_inner { ( $ iter : expr ) => { } ; ( $ iter : expr , ) => { } ; ( $ iter : expr , mut $ var : ident : $ t : tt $ ( $ r : tt ) * ) => { let mut $ var = read_value ! ( $ iter , $ t ) ; input_inner ! { $ iter $ ( $ r ) * } } ; ( $ iter : expr , mut $ var : ident $ ( $ r : tt ) * ) => { let mut $ var = $ iter . next ( ) . unwrap ( ) . parse ::< usize > ( ) . unwrap ( ) ; input_inner ! { $ iter $ ( $ r ) * } } ; ( $ iter : expr , $ var : ident : $ t : tt $ ( $ r : tt ) * ) => { let $ var = read_value ! ( $ iter , $ t ) ; input_inner ! { $ iter $ ( $ r ) * } } ; ( $ iter : expr , $ var : ident $ ( $ r : tt ) * ) => { let $ var = $ iter . next ( ) . unwrap ( ) . parse ::< usize > ( ) . unwrap ( ) ; input_inner ! { $ iter $ ( $ r ) * } } ; }
macro_rules ! read_value { ( $ iter : expr , ( $ ( $ t : tt ) ,* ) ) => { ( $ ( read_value ! ( $ iter , $ t ) ) ,* ) } ; ( $ iter : expr , [ $ t : tt ; $ len : expr ] ) => { ( 0 ..$ len ) . map ( | _ | read_value ! ( $ iter , $ t ) ) . collect ::< Vec < _ >> ( ) } ; ( $ iter : expr , chars ) => { read_value ! ( $ iter , String ) . chars ( ) . collect ::< Vec < char >> ( ) } ; ( $ iter : expr , usize1 ) => { read_value ! ( $ iter , usize ) - 1 } ; ( $ iter : expr , $ t : ty ) => { $ iter . next ( ) . unwrap ( ) . parse ::<$ t > ( ) . unwrap ( ) } ; }
const MOD: i64 = 1_000_000_007;
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
struct Modi64(i64);
impl Modi64 {
    #[inline]
    fn new(i: i64) -> Modi64 {
        Modi64(Modi64::modulo(i, MOD))
    }
    #[inline]
    fn modulo(i: i64, m: i64) -> i64 {
        if i < 0 {
            i % m + m
        } else {
            i % m
        }
    }
    fn pow(self, y: i64) -> Modi64 {
        let mut y = Modi64(Modi64::modulo(y, MOD - 1));
        let mut x = 1.into();
        let mut base = self;
        while y.0 > 0 {
            if y.0 & 1 == 1 {
                x *= base;
            }
            base *= base;
            y = Modi64(y.0 >> 1);
        }
        x
    }
    #[inline]
    fn inv(self) -> Modi64 {
        self.pow(MOD - 2)
    }
}
impl From<i64> for Modi64 {
    fn from(i: i64) -> Modi64 {
        Modi64::new(i)
    }
}
impl std::ops::Add for Modi64 {
    type Output = Modi64;
    fn add(self, rhs: Modi64) -> Modi64 {
        (self.0 + rhs.0).into()
    }
}
impl std::ops::AddAssign for Modi64 {
    fn add_assign(&mut self, rhs: Modi64) {
        *self = *self + rhs;
    }
}
impl std::ops::Sub for Modi64 {
    type Output = Modi64;
    fn sub(self, rhs: Modi64) -> Modi64 {
        (self.0 - rhs.0).into()
    }
}
impl std::ops::SubAssign for Modi64 {
    fn sub_assign(&mut self, rhs: Modi64) {
        *self = *self - rhs;
    }
}
impl std::ops::Mul for Modi64 {
    type Output = Modi64;
    fn mul(self, rhs: Modi64) -> Modi64 {
        (self.0 * rhs.0).into()
    }
}
impl std::ops::MulAssign for Modi64 {
    fn mul_assign(&mut self, rhs: Modi64) {
        *self = *self * rhs;
    }
}
impl std::ops::Div for Modi64 {
    type Output = Modi64;
    fn div(self, rhs: Modi64) -> Modi64 {
        self * rhs.inv()
    }
}
impl std::ops::DivAssign for Modi64 {
    fn div_assign(&mut self, rhs: Modi64) {
        *self = *self / rhs;
    }
}
impl std::ops::Neg for Modi64 {
    type Output = Modi64;
    fn neg(self) -> Modi64 {
        (-self.0).into()
    }
}
impl std::iter::Sum for Modi64 {
    fn sum<I: Iterator<Item = Modi64>>(iter: I) -> Modi64 {
        iter.fold(0.into(), std::ops::Add::add)
    }
}
impl<'a> std::iter::Sum<&'a Modi64> for Modi64 {
    fn sum<I: Iterator<Item = &'a Modi64>>(iter: I) -> Modi64 {
        iter.fold(0.into(), |x, &y| x + y)
    }
}
#[derive(Clone, Debug)]
struct MemorizedFactorial {
    n: usize,
    fact: Vec<Modi64>,
    inv_fact: Vec<Modi64>,
}
impl MemorizedFactorial {
    fn new(max_n: usize) -> MemorizedFactorial {
        let mut fact = vec![1.into(); max_n + 1];
        let mut inv_fact = vec![1.into(); max_n + 1];
        for i in 1..(max_n + 1) {
            fact[i] = fact[i - 1] * (i as i64).into();
            inv_fact[i] = inv_fact[i - 1] / (i as i64).into();
        }
        MemorizedFactorial {
            n: max_n + 1,
            fact: fact,
            inv_fact: inv_fact,
        }
    }
    fn permutation(&self, n: usize, r: usize) -> Modi64 {
        if r <= n {
            self.fact[n] * self.inv_fact[n - r]
        } else {
            0.into()
        }
    }
}
#[derive(Debug)]
struct Rec {
    n: usize,
    k: usize,
    graph: Vec<Vec<usize>>,
    dp: Vec<Modi64>,
    vn1: Vec<usize>,
    fact: MemorizedFactorial,
}
impl Rec {
    fn new(n: usize, k: usize) -> Rec {
        Rec {
            n: n,
            k: k,
            graph: vec![vec![]; n],
            dp: vec![Modi64(0); n],
            vn1: vec![0; n],
            fact: MemorizedFactorial::new(n + k),
        }
    }
    fn add_edge(&mut self, a: usize, b: usize) {
        self.graph[a].push(b);
        self.graph[b].push(a);
    }
    fn solve(&mut self) -> i64 {
        if self.k == 1 {
            return (self.n == 1) as i64;
        }
        let n = self.n;
        self.dfs(0, n);
        (self.dp[0] * (self.k as i64).into()).0
    }
    fn dfs(&mut self, u: usize, p: usize) {
        let k = self.k - (u != 0) as usize;
        for i in 0..self.graph[u].len() {
            let v = self.graph[u][i];
            if v != p {
                self.dfs(v, u);
                self.vn1[u] += 1;
            }
        }
        self.dp[u] = self.fact.permutation(k - 1, self.vn1[u]);
        for i in 0..self.graph[u].len() {
            let v = self.graph[u][i];
            if v != p {
                let d = self.dp[v];
                self.dp[u] *= d;
            }
        }
    }
}
fn main() {
    input! { n, k, ab: [(usize1, usize1); n-1] };
    let mut rec = Rec::new(n, k);
    for &(a, b) in &ab {
        rec.add_edge(a, b);
    }
    println!("{}", rec.solve());
}


Measured memory_bytes: 23292