Theory:

     ‘Oh, nothing very valuable. Marbles I’d won. A book I wasn’t supposed to read. A few old coins I’d collected. Things came and went. I was a bit of a crow, you know, collecting bright things and putting them away. There was my grandfather’s Iron Cross. Well, not my grandfather’s exactly, because he was British and the Iron Cross’ was a German decoration awarded for bravery during the War - the First World War - when my grandfather fought in France. He got it from a German soldier.’
 
     'Do you still have it?’

     ‘No’, he said, looking her in the eyes. ‘I left it in the jackfruit tree.’

     ‘You left it in the tree?’
Explanation:
 
The man said that he did not keep anything important he just kept some marbles which he won. The book he was not supposed to read, was hidden there. Also, a few old coins which he collected. Things whichever he liked. He said he was like a crow, collecting all bright objects and storing them here in the hollow. He said that he had his grandfather's iron cross, which was not his grandfather's exactly. His grandfather was British, and in those days, "Iron cross" was given to only Germans as an award of bravery during the First World War. When his grandfather fought in France, he got it from a German soldier.
 
The girl asked if he still has it.
 
He peeped into her eyes and said that he kept that in the hollow of the jackfruit tree, so he doesn't have it.
 
She asked in astonishment if he left it in that tree.
 
Meanings of difficult words:
 
Number
Word
Meanings
1.
 Decoration  Medal or some award conferred as an honour.
2.
 Valuable Worth a great deal.
3.
  Iron Cross The highest German military decoration for bravery, instituted in 1813.
4.
 Marbles  A small ball of coloured glass or similar material used as a toy.
Reference:
State Council of Educational Research and Training (2018). Term-1 English Standard-9. I Can’t Climb Trees Anymore - Ruskin Bond (Slightly adapted) (pp. 157-160). Published by the Tamil Nadu Textbook and Educational Services Corporation.