。
Look at the bird singing up in the tree.
Literal
Tree [possessive-の] inside [at-で] is-chirping bird [object-を] look-[try-てごらん].
~てごらん is a gentle command/invitation, softer than ~てみて and used especially when speaking to children or as a warm suggestion — 'try X-ing.' さえずる ('to chirp, to twitter') is a specific verb for small birds' songs. 木の中で ('inside the tree,' though more naturally English 'up in the tree') uses で as the location of the singing action.