Tur\'an's Problem for Trees
  For a forbidden graph $L$, let $ex(p;L)$ denote the maximal number of edges in a simple graph of order $p$ not containing $L$. Let $T_n$ denote the unique tree on $n$ vertices with maximal degree $n-2$, and let $T_n^*=(V,E)$ be the tree on $n$ vertices with $V=\{v_0,v_1,\ldots,v_{n-1}\}$ and   $E=\{v_0v_1,\ldots,v_0v_{n-3},v_{n-3}v_{n-2},v_{n-2}v_{n-1}\}$. In the paper we give exact values of $ex(p;T_n)$ and $ex(p;T_n^*)$. 
Zhi-Hong Sun and Lin-Lin Wang
math.CO