"I should prefer to have some boy bend them ...  One by one he subdued his father's trees  By riding them down over and over again  Until he took the stiffness out of them,  And not one but hung limp, not one was left  
"I should prefer to have some boy bend them ...  One by one he subdued his father's trees  By riding them down over and over again  Until he took the stiffness out of them,  And not one but hung limp, not one was left  For him to conquer. ...  One could do worse than be a swinger of", for 10 points, what sort of trees in a poem by Robert Frost?
"I should prefer to have some boy bend them ...  One by one he subdued his father's trees  By riding them down over and over again  Until he took the stiffness out of them,  And not one but hung limp, not one was left  
{Birches}