Insert each node as the left most leaf and check if it is less than the parent or not, if not then swap it with the parent
32
32
/
15
32
/ \
15 20
Now 30 cannot be inserted as 15's child, so it will be in 15's place with 15 as it's child
32
/ \
30 20
/
15
32
/ \
30 20
/ \
15 12
25 cannot be inserted as 20's child, so it will be in place of 20, with 20 as it's child
32
/ \
30 25
/ \ /
15 12 20
32
/ \
30 25
/ \ / \
15 12 20 16