Bill's introduction, stepping on more than one tree (5,7)
I believe the answer is:
first reading
'bill's introduction' is the definition.
'first reading' can be an answer for 'introduction' (thesaurus). I'm not certain of the 'bill's' bit.
'stepping on more than one tree' is the wordplay.
'stepping on' becomes 'treading' (I've seen this in another clue).
'more than' means one lot of letters go next to another.
'one tree' becomes 'firs' (I can't justify this - if you can you should give a lot more credence to this answer).
'treading' after 'firs' is 'FIRST READING'.
Can you help me to learn more?
(Another definition for first reading that I've seen is " Bill's initial appearance".)