With x nodes with degree 1, the number of nodes is *** x+3+ 1+2. Since the number of edges of the tree is the number of nodes minus 1, the number of edges of the tree is x+3+ 1+2- 1, and the total degree of all nodes of the tree is sum.

x+3*2+ 1*3+2*4

The total degree of nodes is equal to twice the number of edges, so the equation is obtained.

x+3 * 2+ 1 * 3+2 * 4 =(x+3+ 1+2- 1)

The solution is x+ 17=2(x+5).

x=7

So there are seven nodes with degree 1.