unidentified small tree

Observation - unidentified small tree. Description: 1-yr old tree,appeared last year in back garden,has grown about 2 ft in one year. Retained quite a lot of leaves over the winter. leaves alternate,long entire.stem smooth, bit reddish at the top. plant pliable. sorry so hard to distinguish in photo. Growi

1-yr old tree,appeared last year in back garden,has grown about 2 ft in one year. Retained quite a lot of leaves over the winter. leaves alternate,long entire.stem smooth, bit reddish at the top. plant pliable. sorry so hard to distinguish in photo. Growing in clayey earth, maybe slightly acid, often flooded when it rains.